Ultimate ROI-Optimized Coding Interview Preparation Guide

Data-Driven Approach for Maximum Interview Success

📊 Overview

This guide organizes coding interview topics by Return on Investment (ROI) and Learning Difficulty based on comprehensive analysis of interview frequency and success rates. Study in the order presented for maximum efficiency.

📊 ROI Methodology & Data Sources

ROI Categories Explained:

High ROI Topics (Study First):

Frequency: 12-25% of interviews
Learning Time: 5-15 hours to competency
Success Impact: High - directly improves interview performance
Examples: Arrays & Hashing, Two Pointers, BFS

Medium ROI Topics (Study Second):

Frequency: 6-12% of interviews
Learning Time: 10-25 hours to competency
Success Impact: Medium - important but more specialized
Examples: Binary Search, Heap, Dynamic Programming

Low ROI Topics (Study Last):

Frequency: 2-6% of interviews
Learning Time: 15-40+ hours to competency
Success Impact: Low - very specialized, high difficulty
Examples: Trie, Union Find, Advanced Greedy

Limitations & Disclaimers:

Data Recency: Based on 2023-2024 interview patterns, may shift over time
Company Variation: ROI may vary significantly by company size, type, and role level
Individual Differences: Learning speeds and prior experience affect time investments
Sample Bias: Data skewed toward tech companies and software engineering roles
Subjective Elements: Success impact ratings based on community consensus

🎯 HIGHEST ROI - Easy to Learn (Study These First!)

1. Arrays & Hashing (Easy to Learn, High ROI)

Why High ROI: Fundamental building blocks, appears in 20-25% of interviews, essential for all other patterns.

Core Concept:

Master array manipulation and hash table operations - the foundation of most coding interview problems.

🎯 Core Problems (Master These First):

Contains Duplicate (Easy) LeetCode [NeetCode-150]
- Time: 10-15 min | Pattern: Hash set for duplicates
Valid Anagram (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Character frequency counting
Two Sum (Easy) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 15-20 min | Pattern: Hash map lookup
Group Anagrams (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Hash map with sorted keys
Top K Frequent Elements (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Frequency counting + sorting
Product of Array Except Self (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Prefix/suffix arrays
Valid Sudoku (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Hash set validation
Longest Consecutive Sequence (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Hash set for O(n) sequence finding

📚 Practice More Arrays & Hashing (6 Additional Problems)

Additional Essential Problems:

Encode And Decode Strings (Medium) LeetCode [NeetCode-150]
First Non-repeating Character (Easy) LeetCode [Coding-Patterns]
Largest Unique Number (Easy) LeetCode [Coding-Patterns]
Maximum Number of Balloons (Easy) LeetCode [Coding-Patterns]
Longest Palindrome (Easy) LeetCode [Coding-Patterns]
Ransom Note (Easy) LeetCode [Coding-Patterns]

Key Patterns:

Hash map for O(1) lookups
Frequency counting with hash maps
Array prefix/suffix techniques
Set operations for duplicates

2. Two Pointers (Easy to Learn, High ROI)

Why High ROI: Appears in 15-20% of interviews, quick to master, builds foundation for other techniques.

Core Concept:

Use two pointers moving towards each other or in the same direction to solve array/string problems efficiently.

🎯 Core Problems (Master These First):

Valid Palindrome (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Opposite direction pointers
Two Sum II - Input Array Is Sorted (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Opposite direction pointers
3Sum (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Fixed + moving pointers
Container With Most Water (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Greedy two pointers
Trapping Rain Water (Hard) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: Advanced two pointers

📚 Practice More Two Pointers (8 Additional Problems)

Additional Essential Problems:

Remove Duplicates from Sorted Array (Easy) LeetCode [Coding-Patterns]
Squares of a Sorted Array (Easy) LeetCode [Coding-Patterns]
3Sum Closest (Medium) LeetCode [Coding-Patterns]
4Sum (Medium) LeetCode [Coding-Patterns]
Subarray Product Less Than K (Medium) LeetCode [Coding-Patterns]

Fast & Slow Pointers (Cycle Detection):

Linked List Cycle (Easy) LeetCode [Coding-Patterns, NeetCode-150]
Find the Duplicate Number (Medium) LeetCode [NeetCode-150]
Happy Number (Medium) LeetCode [Coding-Patterns]

Key Patterns:

Opposite direction pointers (palindrome, two sum)
Same direction pointers (remove duplicates)
Fast & slow pointers (cycle detection)

3. Sliding Window (Easy to Learn, High ROI)

Why High ROI: 10-15% of interviews, excellent for string/array optimization problems.

Core Concept:

Maintain a window of elements and slide it to find optimal solutions without recalculating from scratch.

🎯 Core Problems (Master These First):

Best Time to Buy and Sell Stock (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Simple sliding window
Longest Substring Without Repeating Characters (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Variable window with hash set
Longest Repeating Character Replacement (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Variable window with frequency count
Permutation in String (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Fixed window with frequency matching
Minimum Window Substring (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Advanced variable window

📚 Practice More Sliding Window (7 Additional Problems)

Additional Essential Problems:

Maximum Sum Subarray of Size K (Easy) [Coding-Patterns]
Find All Anagrams in a String (Medium) LeetCode [Coding-Patterns]
Fruit Into Baskets (Medium) LeetCode [Coding-Patterns]
Longest Substring with K Distinct Characters (Medium) [Coding-Patterns]
Smallest Subarray with Given Sum (Easy) [Coding-Patterns]
Sliding Window Maximum (Hard) LeetCode [NeetCode-150]
Longest Subarray with Ones after Replacement (Hard) LeetCode [Coding-Patterns]

Key Patterns:

Fixed-size window
Variable-size window
Window with character frequency tracking

4. Stack & Queue (Easy to Learn, High ROI)

Why High ROI: Appears in 12-15% of interviews, essential for parsing and monotonic problems.

Core Concept:

Use LIFO (stack) and FIFO (queue) data structures to solve parsing, matching, and ordering problems.

🎯 Core Problems (Master These First):

Valid Parentheses (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Stack for matching pairs
Min Stack (Easy) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Auxiliary stack for min tracking
Evaluate Reverse Polish Notation (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Stack for expression evaluation
Daily Temperatures (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Monotonic stack
Largest Rectangle in Histogram (Hard) LeetCode [NeetCode-150]
- Time: 35-40 min | Pattern: Advanced monotonic stack

📚 Practice More Stack & Queue (2 Additional Problems)

Additional Essential Problems:

Generate Parentheses (Medium) LeetCode [NeetCode-150]
Car Fleet (Medium) LeetCode [NeetCode-150]

Key Patterns:

Stack for matching and parsing
Monotonic stack for next greater/smaller
Queue for level-order processing
Design problems with stacks

5. Breadth-First Search (Easy to Learn, High ROI)

Why High ROI: Fundamental for tree/graph problems, appears in 12-18% of interviews.

Core Concept:

Explore nodes level by level using a queue. Essential for shortest path and level-order problems.

🎯 Core Problems (Master These First):

Binary Tree Level Order Traversal (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Basic level-order traversal
Maximum Depth of Binary Tree (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: BFS depth counting
Number of Islands (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Grid BFS
Rotting Oranges (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Multi-source BFS
Course Schedule (Medium) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: Topological sort with BFS

📚 Practice More BFS (10 Additional Problems)

Tree BFS Problems:

Minimum Depth of Binary Tree (Easy) LeetCode [Coding-Patterns]
Average of Levels in Binary Tree (Easy) LeetCode [Coding-Patterns]
Binary Tree Level Order Traversal II (Medium) LeetCode [Coding-Patterns]
Binary Tree Zigzag Level Order Traversal (Medium) LeetCode [Coding-Patterns]
Binary Tree Right Side View (Medium) LeetCode [Coding-Patterns, NeetCode-150]
Populating Next Right Pointers in Each Node (Medium) LeetCode [Coding-Patterns]

Graph BFS Problems:

Walls and Gates (Medium) LeetCode [NeetCode-150]
Clone Graph (Medium) LeetCode [NeetCode-150]
Word Ladder (Hard) LeetCode [NeetCode-150]
Alien Dictionary (Hard) LeetCode [NeetCode-150]

Key Patterns:

Level-order traversal
Shortest path in unweighted graphs
Multi-source BFS

🔥 HIGHEST ROI - Medium/High Difficulty (Study These Second)

6. Depth-First Search (Medium to Learn, High ROI)

Why High ROI: Core technique for trees/graphs, backtracking foundation. 15-25% of interviews.

Core Concept:

Explore as far as possible along each branch before backtracking. Essential for tree traversals and path problems.

🎯 Core Problems (Master These First):

Invert Binary Tree (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Tree transformation
Validate Binary Search Tree (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Tree validation with bounds
Diameter of Binary Tree (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Tree metrics calculation
Course Schedule (Medium) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: Cycle detection in directed graph
Binary Tree Maximum Path Sum (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Advanced tree path problems

📚 Practice More DFS (15 Additional Problems)

Tree DFS Problems:

Same Tree (Easy) LeetCode [NeetCode-150]
Path Sum (Easy) LeetCode [Coding-Patterns]
Subtree of Another Tree (Easy) LeetCode [NeetCode-150]
Balanced Binary Tree (Easy) LeetCode [NeetCode-150]
Kth Smallest Element in a BST (Medium) LeetCode [NeetCode-150]
Construct Binary Tree from Preorder and Inorder Traversal (Medium) LeetCode [NeetCode-150]
Path Sum II (Medium) LeetCode [Coding-Patterns]
Path Sum III (Medium) LeetCode
Sum Root to Leaf Numbers (Medium) LeetCode [Coding-Patterns]
Lowest Common Ancestor of a Binary Tree (Medium) LeetCode [NeetCode-150]
House Robber III (Medium) LeetCode [NeetCode-150]
Serialize and Deserialize Binary Tree (Hard) LeetCode [NeetCode-150]

Graph DFS Problems:

Clone Graph (Medium) LeetCode [NeetCode-150]
Course Schedule II (Medium) LeetCode [NeetCode-150]
Pacific Atlantic Water Flow (Medium) LeetCode [NeetCode-150]

Key Patterns:

Tree traversals (preorder, inorder, postorder)
Path sum problems
Graph cycle detection
Topological sorting

7. Backtracking (High Difficulty to Learn, High ROI)

Why High ROI: Appears in 8-12% of interviews, but critical for senior roles and complex problem-solving.

Core Concept:

Systematically explore all possible solutions by building candidates incrementally and abandoning those that cannot lead to a valid solution.

🎯 Core Problems (Master These First):

Subsets (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Generate all combinations
Permutations (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Generate all arrangements
Combination Sum (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Target sum with reuse
Word Search (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Grid backtracking
Generate Parentheses (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Constraint-based generation
N-Queens (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Constraint satisfaction

📚 Practice More Backtracking (6 Additional Problems)

Additional Essential Problems:

Subsets II (Medium) LeetCode [NeetCode-150]
Combination Sum II (Medium) LeetCode [NeetCode-150]
Palindrome Partitioning (Medium) LeetCode [NeetCode-150]
Letter Combinations of a Phone Number (Medium) LeetCode [NeetCode-150]
Sudoku Solver (Hard) LeetCode [Coding-Patterns]
Word Search II (Hard) LeetCode [NeetCode-150]

Key Patterns:

Generate all combinations/permutations
Constraint satisfaction problems
Path finding with constraints
Decision tree exploration

📊 Progress Tracking - High ROI Topics

🎯 Study Plan Recommendations

1-2 Weeks (Crash Course)

Focus ONLY on Easy + High ROI topics:

Arrays & Hashing (2-3 days) - 8 core problems
Two Pointers (2-3 days) - 5 core problems
Sliding Window (2-3 days) - 5 core problems
Stack & Queue (1-2 days) - 5 core problems
Breadth-First Search (2-3 days) - 5 core problems

Expected Outcome: Cover 45-60% of common interview patterns

1 Month (Balanced Approach)

Complete all High ROI topics:

Week 1: Arrays & Hashing + Two Pointers
Week 2: Sliding Window + Stack & Queue
Week 3: Breadth-First Search + Basic DFS
Week 4: Advanced DFS + Backtracking fundamentals

Expected Outcome: Cover 70-85% of interview patterns

2+ Months (Comprehensive)

Add Medium ROI topics after mastering High ROI:

Month 1: All High ROI topics (complete mastery)
Month 2: Binary Search + Heap + Intervals
Month 3+: Dynamic Programming + Linked Lists + Low ROI topics
Focus on depth over breadth
Practice system design integration

Continue to Medium ROI section after mastering these High ROI topics...

💪 MEDIUM ROI - Study These Third

8. Binary Search (Easy to Learn, Medium ROI)

Why Medium ROI: Appears in 8-12% of interviews, but essential for optimization problems.

Core Concept:

Efficiently search sorted arrays or search spaces by repeatedly dividing the problem in half.

🎯 Core Problems (Master These First):

Binary Search (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Classic binary search
Search in Rotated Sorted Array (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Modified binary search
Find Minimum in Rotated Sorted Array (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Find pivot in rotated array
Koko Eating Bananas (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Binary search on answer
Median of Two Sorted Arrays (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Advanced binary search

📚 Practice More Binary Search (10 Additional Problems)

Additional Essential Problems:

Search a 2D Matrix (Medium) LeetCode [Coding-Patterns, NeetCode-150]
Time Based Key-Value Store (Medium) LeetCode [NeetCode-150]
Find First and Last Position of Element in Sorted Array (Medium) LeetCode [Coding-Patterns]
Search in Rotated Sorted Array II (Medium) LeetCode [Coding-Patterns]
Find Peak Element (Medium) LeetCode [Coding-Patterns]
Capacity To Ship Packages Within D Days (Medium) LeetCode [Coding-Patterns]
Minimum Number of Days to Make m Bouquets (Medium) LeetCode [Coding-Patterns]
Sqrt(x) (Easy) LeetCode [NeetCode-150]
Pow(x, n) (Medium) LeetCode [NeetCode-150]
Search Bitonic Array (Medium) LeetCode [Coding-Patterns]

Key Patterns:

Classic binary search on sorted arrays
Binary search on rotated arrays
Binary search on answer (optimization problems)
2D matrix search

9. Heap (Medium to Learn, Medium ROI)

Why Medium ROI: 6-10% of interviews, crucial for priority-based problems and top-K scenarios.

Core Concept:

Use heap data structure to efficiently maintain ordered elements and solve priority-based problems.

🎯 Core Problems (Master These First):

Kth Largest Element in a Stream (Easy) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Min heap for top K
Last Stone Weight (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Max heap simulation
K Closest Points to Origin (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Min heap with custom comparator
Top K Frequent Elements (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Frequency counting + heap
Find Median from Data Stream (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Two heaps (max + min)

📚 Practice More Heap (2 Additional Problems)

Additional Essential Problems:

Merge k Sorted Lists (Hard) LeetCode [Coding-Patterns, NeetCode-150]
Task Scheduler (Medium) LeetCode [NeetCode-150]

Key Patterns:

Top K elements
Two heaps (median finding)
K-way merge
Priority scheduling

10. Intervals (Medium to Learn, Medium ROI)

Why Medium ROI: Appears in 8-12% of interviews, essential for scheduling and time-based problems.

Core Concept:

Work with time intervals, ranges, and overlapping periods to solve scheduling, merging, and optimization problems.

🎯 Core Problems (Master These First):

Merge Intervals (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Sort and merge overlapping intervals
Insert Interval (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Insert and merge in sorted intervals
Non Overlapping Intervals (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Greedy interval scheduling
Meeting Rooms (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Check for overlapping intervals
Meeting Rooms II (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Minimum rooms needed

📚 Practice More Intervals (3 Additional Problems)

Additional Essential Problems:

Intervals Intersection (Medium) LeetCode [Coding-Patterns]
Maximum CPU Load (Hard) GeeksforGeeks [Coding-Patterns]
Employee Free Time (Hard) LeetCode [Coding-Patterns]

Key Patterns:

Sort intervals by start time
Merge overlapping intervals
Greedy scheduling algorithms
Priority queue for interval management

11. Cyclic Sort (Easy to Learn, Medium ROI)

Why Medium ROI: Appears in 6-10% of interviews, specialized but efficient pattern for array problems.

Core Concept:

Sort arrays containing numbers in a given range by placing each number at its correct index position.

🎯 Core Problems (Master These First):

Missing Number (Easy) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 15-20 min | Pattern: Cyclic sort to find missing
Find the Duplicate Number (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 20-25 min | Pattern: Cyclic sort or Floyd's algorithm
Find All Numbers Disappeared in an Array (Easy) LeetCode [Coding-Patterns]
- Time: 20-25 min | Pattern: Mark visited indices
Find All Duplicates in an Array (Medium) LeetCode [Coding-Patterns]
- Time: 20-25 min | Pattern: Mark visited with negation
First Missing Positive (Hard) LeetCode [Coding-Patterns]
- Time: 30-35 min | Pattern: Cyclic sort with constraints

📚 Practice More Cyclic Sort (4 Additional Problems)

Additional Essential Problems:

Cyclic Sort (Easy) GeeksforGeeks [Coding-Patterns]
Find the Corrupt Pair (Easy) TheCodingSimplified [Coding-Patterns]
Find the First K Missing Positive Numbers (Hard) TheCodingSimplified [Coding-Patterns]
Smallest Missing Positive Number (Medium) LeetCode [Coding-Patterns]

Key Patterns:

Place elements at correct indices
Use array indices as hash map
Mark visited elements
Handle duplicates and missing numbers

12. K-way Merge (Medium to Learn, Medium ROI)

Why Medium ROI: Appears in 5-8% of interviews, important for merge operations and priority queues.

Core Concept:

Merge multiple sorted arrays or lists using heap/priority queue for efficient sorting.

🎯 Core Problems (Master These First):

Merge k Sorted Lists (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Min heap for k-way merge
Kth Smallest Element in a Sorted Matrix (Medium) LeetCode [Coding-Patterns]
- Time: 25-30 min | Pattern: Min heap with matrix traversal
Smallest Range Covering Elements from K Lists (Hard) LeetCode [Coding-Patterns]
- Time: 35-40 min | Pattern: Min heap with range tracking

📚 Practice More K-way Merge (3 Additional Problems)

Additional Essential Problems:

Kth Smallest Number in M Sorted Lists (Medium) GeeksforGeeks [Coding-Patterns]
K Pairs with Largest Sums (Medium) LeetCode [Coding-Patterns]
Merge Sorted Array (Easy) LeetCode [NeetCode-150]

Key Patterns:

Min heap for k-way merge
Priority queue with custom comparators
Merge multiple sorted sequences
Kth element in merged result

13. Dynamic Programming (High Difficulty to Learn, Medium ROI)

Why Medium ROI: 10-15% of interviews, but high difficulty makes it lower ROI for time-constrained prep.

Core Concept:

Break down complex problems into simpler subproblems and store results to avoid redundant calculations.

🎯 Core Problems (Master These First):

Climbing Stairs (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Basic 1-D DP
House Robber (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Decision-based DP
Coin Change (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Unbounded knapsack
Unique Paths (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: 2-D grid DP
Longest Common Subsequence (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: 2-D string DP

📚 Practice More Dynamic Programming (8 Additional Problems)

1-D DP Problems:

House Robber II (Medium) LeetCode [NeetCode-150]
Longest Increasing Subsequence (Medium) LeetCode [NeetCode-150]
Word Break (Medium) LeetCode [NeetCode-150]
Decode Ways (Medium) LeetCode [NeetCode-150]

2-D DP Problems:

Edit Distance (Hard) LeetCode [NeetCode-150]
Partition Equal Subset Sum (Medium) LeetCode [Coding-Patterns, NeetCode-150]
0/1 Knapsack (Medium) GeeksforGeeks [Coding-Patterns]
Target Sum (Medium) LeetCode [NeetCode-150]

Key Patterns:

1-D DP (linear problems)
2-D DP (grid/string problems)
Knapsack variations
State machine DP

📚 LOW ROI - Study These Last (Time Permitting)

11. Linked Lists (Easy to Learn, Medium ROI)

Why Medium ROI: 6-10% of interviews, fundamental data structure with many variations.

Core Concept:

Master linked list manipulation, pointer techniques, and common operations for dynamic data structures.

🎯 Core Problems (Master These First):

Reverse Linked List (Easy) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 15-20 min | Pattern: Iterative pointer reversal
Merge Two Sorted Lists (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Two-pointer merging
Linked List Cycle (Easy) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 15-20 min | Pattern: Fast & slow pointers
Remove Nth Node From End of List (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Two-pointer with gap
Reorder List (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Find middle + reverse + merge
Add Two Numbers (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Digit-by-digit addition with carry
Copy List With Random Pointer (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Hash map for node mapping

📚 Practice More Linked Lists (8 Additional Problems)

Advanced Linked List Problems:

Reverse Linked List II (Medium) LeetCode [Coding-Patterns]
Reverse Nodes in k-Group (Hard) LeetCode [Coding-Patterns, NeetCode-150]
Rotate List (Medium) LeetCode [Coding-Patterns]
Palindrome Linked List (Easy) LeetCode [Coding-Patterns]
Merge k Sorted Lists (Hard) LeetCode [NeetCode-150]
LRU Cache (Medium) LeetCode [NeetCode-150]
Linked List Cycle II (Medium) LeetCode [Coding-Patterns]
Middle of the Linked List (Easy) LeetCode [Coding-Patterns]

Key Patterns:

Pointer manipulation and reversal
Two-pointer techniques (fast/slow, gap)
Dummy node usage for edge cases
Hash map for complex node relationships

12. Bit Manipulation (Easy to Learn, Low ROI)

Why Low ROI: 3-5% of interviews, quick to master but rarely appears.

Essential Problems:

Single Number (Easy) LeetCode [NeetCode-150]
Number of 1 Bits (Easy) LeetCode [NeetCode-150]
Counting Bits (Easy) LeetCode [NeetCode-150]
Missing Number (Easy) LeetCode [NeetCode-150]
Reverse Bits (Easy) LeetCode [NeetCode-150]

Key Patterns:

XOR for finding unique elements
Bit masking and manipulation
Power of 2 operations

13. Trie (Medium to Learn, Low ROI)

Why Low ROI: 2-4% of interviews, specialized use cases.

Essential Problems:

Implement Trie (Prefix Tree) (Medium) LeetCode [Coding-Patterns, NeetCode-150]
Design Add and Search Words Data Structure (Medium) LeetCode [NeetCode-150]
Word Search II (Hard) LeetCode [NeetCode-150]

Key Patterns:

Prefix matching
Auto-complete systems
Word games and puzzles

14. Union Find (Medium to Learn, Low ROI)

Why Low ROI: 2-3% of interviews, very specialized.

Essential Problems:

Number of Connected Components in an Undirected Graph (Medium) LeetCode [NeetCode-150]
Redundant Connection (Medium) LeetCode [Coding-Patterns, NeetCode-150]

Key Patterns:

Connected components
Cycle detection in undirected graphs
Dynamic connectivity

15. Math & Geometry (Medium to Learn, Low ROI)

Why Low ROI: 3-5% of interviews, specialized mathematical problems.

Core Concept:

Solve problems involving mathematical calculations, geometric operations, and matrix manipulations.

🎯 Core Problems (Master These First):

Rotate Image (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Matrix rotation in-place
Spiral Matrix (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Matrix traversal with boundaries
Set Matrix Zeroes (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Matrix modification with space optimization
Plus One (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Array arithmetic with carry
Multiply Strings (Medium) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: String arithmetic simulation

📚 Practice More Math & Geometry (3 Additional Problems)

Additional Essential Problems:

Happy Number (Easy) LeetCode [NeetCode-150]
Pow(x, n) (Medium) LeetCode [NeetCode-150]
Detect Squares (Medium) LeetCode [NeetCode-150]

Key Patterns:

Matrix manipulation and traversal
Mathematical simulation
Geometric calculations
Number theory problems

16. Advanced Graphs (High to Learn, Low ROI)

Why Low ROI: 2-4% of interviews, very specialized graph algorithms.

Core Concept:

Advanced graph algorithms including shortest paths, minimum spanning trees, and complex graph traversals.

🎯 Core Problems (Master These First):

Network Delay Time (Medium) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: Dijkstra's shortest path
Min Cost to Connect All Points (Medium) LeetCode [NeetCode-150]
- Time: 30-35 min | Pattern: Minimum spanning tree (Prim's)
Cheapest Flights Within K Stops (Medium) LeetCode [NeetCode-150]
- Time: 35-40 min | Pattern: Modified Dijkstra with constraints

📚 Practice More Advanced Graphs (3 Additional Problems)

Additional Essential Problems:

Reconstruct Itinerary (Hard) LeetCode [NeetCode-150]
Swim In Rising Water (Hard) LeetCode [NeetCode-150]
Alien Dictionary (Hard) LeetCode [NeetCode-150]

Key Patterns:

Dijkstra's algorithm
Minimum spanning tree (Prim's/Kruskal's)
Bellman-Ford algorithm
Advanced graph traversal

17. Topological Sort (Medium to Learn, Low ROI)

Why Low ROI: 2-3% of interviews, specialized for dependency problems.

Core Concept:

Order vertices in a directed acyclic graph such that for every directed edge, the source comes before the destination.

🎯 Core Problems (Master These First):

Course Schedule (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Cycle detection with topological sort
Course Schedule II (Medium) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 25-30 min | Pattern: Topological ordering
Alien Dictionary (Hard) LeetCode [Coding-Patterns, NeetCode-150]
- Time: 35-40 min | Pattern: Build graph from constraints

📚 Practice More Topological Sort (5 Additional Problems)

Additional Essential Problems:

Minimum Height Trees (Medium) LeetCode [Coding-Patterns]
Sequence Reconstruction (Medium) LeetCode [Coding-Patterns]
All Ancestors of a Node in a Directed Acyclic Graph (Medium) LeetCode
Find All Possible Recipes from Given Supplies (Medium) LeetCode
Parallel Courses (Medium) LeetCode

Key Patterns:

Kahn's algorithm (BFS-based)
DFS-based topological sort
Cycle detection in directed graphs
Dependency resolution

18. String Manipulation (Easy to Learn, Low ROI)

Why Low ROI: 4-6% of interviews, often covered in other topics.

Core Concept:

Advanced string processing, pattern matching, and text manipulation algorithms.

🎯 Core Problems (Master These First):

Longest Palindromic Substring (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Expand around centers
Palindromic Substrings (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Count palindromes
Valid Palindrome II (Easy) LeetCode [Coding-Patterns]
- Time: 20-25 min | Pattern: Palindrome with one deletion
Implement strStr() (Easy) LeetCode [Coding-Patterns]
- Time: 20-25 min | Pattern: String matching (KMP)

📚 Practice More String Manipulation (4 Additional Problems)

Additional Essential Problems:

String to Integer (atoi) (Medium) LeetCode
Reverse Words in a String (Medium) LeetCode
Longest Common Prefix (Easy) LeetCode
Valid Number (Hard) LeetCode

Key Patterns:

Palindrome detection and expansion
String parsing and validation
Pattern matching algorithms
Text processing and manipulation

19. Greedy (High Difficulty to Learn, Low ROI)

Why Low ROI: 4-6% of interviews, but high difficulty and problem-specific nature makes it low ROI.

Core Concept:

Make locally optimal choices at each step to find a global optimum.

🎯 Core Problems (Master These First):

Maximum Subarray (Easy) LeetCode [NeetCode-150]
- Time: 15-20 min | Pattern: Kadane's algorithm
Jump Game (Medium) LeetCode [NeetCode-150]
- Time: 20-25 min | Pattern: Greedy reachability
Jump Game II (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Greedy minimum jumps
Gas Station (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Greedy circular array
Hand of Straights (Medium) LeetCode [NeetCode-150]
- Time: 25-30 min | Pattern: Greedy grouping

📚 Practice More Greedy (8 Additional Problems)

Additional Essential Problems:

Valid Parenthesis String (Medium) LeetCode [NeetCode-150]
Partition Labels (Medium) LeetCode [NeetCode-150]
Merge Triplets to Form Target Triplet (Medium) LeetCode [NeetCode-150]
Valid Palindrome II (Easy) LeetCode [Coding-Patterns]
Maximum Length of Pair Chain (Medium) LeetCode [Coding-Patterns]
Minimum Add to Make Parentheses Valid (Medium) LeetCode [Coding-Patterns]
Remove Duplicate Letters (Medium) LeetCode [Coding-Patterns]
Largest Palindromic Number (Medium) LeetCode [Coding-Patterns]

Key Patterns:

Local optimal choices leading to global optimum
Interval scheduling and activity selection
Greedy choice property
Optimization problems

📊 Complete Progress Tracking

High ROI Topics (Priority 1) ⭐⭐⭐⭐⭐

Arrays & Hashing (Easy) - 8/8 problems completed
Two Pointers (Easy) - 5/5 problems completed
Sliding Window (Easy) - 5/5 problems completed
Stack & Queue (Easy) - 5/5 problems completed
Breadth-First Search (Easy) - 5/5 problems completed
Depth-First Search (Medium) - 5/5 problems completed
Backtracking (High) - 6/6 problems completed

High ROI Completion: /7 topics (_%)

Medium ROI Topics (Priority 2) ⭐⭐⭐

Binary Search (Easy) - 5/5 problems completed
Heap (Medium) - 5/5 problems completed
Intervals (Medium) - 5/5 problems completed
Cyclic Sort (Easy) - 5/5 problems completed
K-way Merge (Medium) - 3/3 problems completed
Dynamic Programming (High) - 5/5 problems completed

Medium ROI Completion: /6 topics (_%)

Low ROI Topics (Priority 3) ⭐

Linked Lists (Medium) - 7/7 problems completed
Bit Manipulation (Easy) - 5/5 problems completed
Trie (Medium) - 3/3 problems completed
Union Find (Medium) - 2/2 problems completed
Math & Geometry (Medium) - 5/5 problems completed
Advanced Graphs (High) - 3/3 problems completed
Topological Sort (Medium) - 3/3 problems completed
String Manipulation (Easy) - 4/4 problems completed
Greedy (High) - 5/5 problems completed

Low ROI Completion: /9 topics (_%)

🎯 Final Study Recommendations

Time-Based Mastery Paths

🚀 1-2 Weeks (Emergency Prep)

Goal: Cover highest-impact topics only

Days 1-3: Arrays & Hashing + Two Pointers (8+5 core problems)
Days 4-6: Sliding Window + Stack & Queue (5+5 core problems)
Days 7-10: BFS basics (5 core problems)
Expected Coverage: 50-65% of interview patterns
Success Rate: Good for junior/mid-level positions

📅 1 Month (Balanced Prep)

Goal: Master all high ROI topics

Week 1: Arrays & Hashing + Two Pointers (complete)
Week 2: Sliding Window + Stack & Queue (complete)
Week 3: BFS + DFS basics
Week 4: Advanced DFS + Backtracking fundamentals
Expected Coverage: 75-85% of interview patterns
Success Rate: Good for most positions

📚 2+ Months (Comprehensive Prep)

Goal: Complete mastery including medium and low ROI

Month 1: All High ROI topics (complete mastery)
Month 2: Binary Search + Heap + Intervals + Cyclic Sort + K-way Merge
Month 3: Dynamic Programming + Linked Lists
Month 4+: All Low ROI topics for 100% coverage
Expected Coverage: 95-100% of interview patterns
Success Rate: Excellent for senior positions and FAANG

🎖️ Mastery Milestones

Beginner → Intermediate:

Complete all High ROI Easy topics (Arrays, Two Pointers, Sliding Window, Stack & Queue, BFS)
Solve 25+ problems across these topics
Can recognize patterns quickly

Intermediate → Advanced:

Complete all High ROI topics including DFS and Backtracking
Solve 40+ problems across High ROI topics
Can solve medium problems independently

Advanced → Expert:

Complete High + Medium ROI topics
Solve 60+ problems across all covered topics
Can tackle hard problems and optimize solutions

📖 Source Attribution

This guide consolidates content from:

Coding Interview Patterns (28 patterns) - Comprehensive pattern-based approach
NeetCode-150 (18 categories) - Curated problem selection
AlgoMonster ROI Analysis - Data-driven prioritization

Methodology: Problems were consolidated across sources, duplicates removed, and organized by ROI data to create the most efficient study path possible.

🔗 Quick Reference Links

LeetCode - Primary practice platform
NeetCode YouTube - Video explanations
AlgoMonster - Pattern-based learning
Educative.io - Interactive courses

Remember: Focus on understanding patterns over memorizing solutions. The ROI-based approach ensures you're studying the most impactful topics first. Consistency beats intensity - study regularly and track your progress!

Good luck with your interviews! 🚀

Name		Name	Last commit message	Last commit date
Latest commit History 5 Commits
.github		.github
README.md		README.md

interview-cracking/InterviewPrep

Folders and files

Latest commit

History

Repository files navigation

Ultimate ROI-Optimized Coding Interview Preparation Guide

📊 Overview

📊 ROI Methodology & Data Sources

ROI Categories Explained:

High ROI Topics (Study First):

Medium ROI Topics (Study Second):

Low ROI Topics (Study Last):

Limitations & Disclaimers:

🎯 HIGHEST ROI - Easy to Learn (Study These First!)

1. Arrays & Hashing (Easy to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

2. Two Pointers (Easy to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Fast & Slow Pointers (Cycle Detection):

Key Patterns:

3. Sliding Window (Easy to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

4. Stack & Queue (Easy to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

5. Breadth-First Search (Easy to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Tree BFS Problems:

Graph BFS Problems:

Key Patterns:

🔥 HIGHEST ROI - Medium/High Difficulty (Study These Second)

6. Depth-First Search (Medium to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Tree DFS Problems:

Graph DFS Problems:

Key Patterns:

7. Backtracking (High Difficulty to Learn, High ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

📊 Progress Tracking - High ROI Topics

🎯 Study Plan Recommendations

1-2 Weeks (Crash Course)

1 Month (Balanced Approach)

2+ Months (Comprehensive)

8. Binary Search (Easy to Learn, Medium ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

9. Heap (Medium to Learn, Medium ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

10. Intervals (Medium to Learn, Medium ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

11. Cyclic Sort (Easy to Learn, Medium ROI)

Core Concept:

🎯 Core Problems (Master These First):

Additional Essential Problems:

Key Patterns:

12. K-way Merge (Medium to Learn, Medium ROI)

Core Concept: