Grind 75

Table of Contents

1. Array
   1. Two Sum
   2. Best Time to Buy and Sell Stock
   3. Majority Element
   4. Contains Duplicate
   5. Meeting Rooms
   6. Move Zeroes
   7. Squares of a Sorted Array
   8. Insert Interval
   9. 3Sum
   10. Product of Array Except Self
   11. Combination Sum
   12. Merge Intervals
   13. Sort Colors
   14. Container With Most Water
   15. Gas Station
   16. Longest Consecutive Sequence
   17. Rotate Array
   18. Contiguous Array
   19. Subarray Sum Equals K
   20. Meeting Rooms II
   21. 3Sum Closest
   22. Non-overlapping Intervals
   23. Employee Free Time
   24. Sliding Window Maximum
2. Stack
   1. Valid Parentheses
   2. Implement Queue using Stacks
   3. Min Stack
   4. Backspace String Compare
   5. Evaluate Reverse Polish Notation
   6. Daily Temperatures
   7. Decode String
   8. Asteroid Collision
   9. Basic Calculator II
   10. Trapping Rain Water
   11. Basic Calculator
   12. Largest Rectangle in Histogram
   13. Maximum Frequency Stack
   14. Longest Valid Parentheses
3. Linked List
   1. Merge Two Sorted Lists
   2. Linked List Cycle
   3. Reverse Linked List
   4. Middle of the Linked List
   5. Palindrome Linked List
   6. LRU Cache
   7. Remove Nth Node From End of List
   8. Swap Nodes in Pairs
   9. Odd Even Linked List
   10. Add Two Numbers
   11. Sort List
   12. Reorder List
   13. Rotate List
   14. Reverse Nodes in k-Group
4. String
   1. Valid Palindrome
   2. Valid Anagram
   3. Longest Palindrome
   4. Longest Common Prefix
   5. Longest Substring Without Repeating Characters
   6. String to Integer (atoi)
   7. Longest Palindromic Substring
   8. Find All Anagrams in a String
   9. Group Anagrams
   10. Longest Repeating Character Replacement
   11. Largest Number
   12. Encode and Decode Strings
   13. Minimum Window Substring
   14. Palindrome Pairs
5. Binary Tree
   1. Invert Binary Tree
   2. Balanced Binary Tree
   3. Diameter of Binary Tree
   4. Maximum Depth of Binary Tree
   5. Same Tree
   6. Symmetric Tree
   7. Subtree of Another Tree
   8. Binary Tree Level Order Traversal
   9. Lowest Common Ancestor of a Binary Tree
   10. Binary Tree Right Side View
   11. Construct Binary Tree from Preorder and Inorder Traversal
   12. Path Sum II
   13. Maximum Width of Binary Tree
   14. Binary Tree Zigzag Level Order Traversal
   15. Path Sum III
   16. All Nodes Distance K in Binary Tree
   17. Serialize and Deserialize Binary Tree
   18. Binary Tree Maximum Path Sum
6. Binary Search
   1. Binary Search
   2. First Bad Version
   3. Search in Rotated Sorted Array
   4. Time Based Key-Value Store
   5. Search a 2D Matrix
   6. Find Minimum in Rotated Sorted Array
   7. Maximum Profit in Job Scheduling
   8. Median of Two Sorted Arrays
7. Graph
   1. Flood Fill
   2. 01 Matrix
   3. Clone Graph
   4. Course Schedule
   5. Number of Islands
   6. Rotting Oranges
   7. Accounts Merge
   8. Word Search
   9. Minimum Height Trees
   10. Pacific Atlantic Water Flow
   11. Shortest Path to Get Food
   12. Graph Valid Tree
   13. Course Schedule II
   14. Number of Connected Components in an Undirected Graph
   15. Minimum Knight Moves
   16. Cheapest Flights Within K Stops
   17. Word Ladder
   18. Longest Increasing Path in a Matrix
   19. Word Search II
   20. Alien Dictionary
   21. Bus Routes
8. Dynamic Programming
   1. Maximum Subarray
   2. Climbing Stairs
   3. Coin Change
   4. Partition Equal Subset Sum
   5. Unique Paths
   6. House Robber
   7. Maximum Product Subarray
   8. Longest Increasing Subsequence
   9. Jump Game
   10. Maximal Square
   11. Decode Ways
   12. Combination Sum IV
9. Binary Search Tree
   1. Lowest Common Ancestor of a Binary Search Tree
   2. Convert Sorted Array to Binary Search Tree
   3. Validate Binary Search Tree
   4. Kth Smallest Element in a BST
   5. Inorder Successor in BST
10. Hash Table
    1. Ransom Note
    2. Insert Delete GetRandom O(1)
    3. First Missing Positive
11. Binary
    1. Add Binary
    2. Counting Bits
    3. Number of 1 Bits
    4. Single Number
    5. Missing Number
    6. Reverse Bits
    7. Find the Duplicate Number
12. Math
    1. Roman to Integer
    2. Palindrome Number
    3. Random Pick with Weight
    4. Pow(x, n)
    5. Reverse Integer
13. Heap
    1. K Closest Points to Origin
    2. Task Scheduler
    3. Top K Frequent Words
    4. Find K Closest Elements
    5. Kth Largest Element in an Array
    6. Find Median from Data Stream
    7. Merge k Sorted Lists
    8. Smallest Range Covering Elements from K Lists
14. Trie
    1. Implement Trie (Prefix Tree)
    2. Word Break
    3. Design Add and Search Words Data Structure
    4. Design In-Memory File System
15. Recursion
    1. Permutations
    2. Subsets
    3. Letter Combinations of a Phone Number
    4. Next Permutation
    5. Generate Parentheses
    6. N-Queens
16. Matrix
    1. Spiral Matrix
    2. Valid Sudoku
    3. Rotate Image
    4. Set Matrix Zeroes
    5. Sudoku Solver
17. Queue
    1. Design Hit Counter

Array

1. Two Sum

   Leetcode
   Initialize hashmap with element as key and index as value. Iterate through array checking if target number minus current element in hashmap. If yes, return indexes of both elements from hashmap

2. Best Time to Buy and Sell Stock

   Leetcode
   Use sliding window to keep track of start index and end = start + 1 index. Keep track of max and current profit starting at 0. If end - start less than 0, update start to end and end to start + 1. Else, if end - start > max profit, update max profit and move end to next element.

3. Majority Element

   Leetcode
   Use hashmap to keep count of how many times an element appears in array, then iterate over hashmap and return element with a count > ceiling(n/2)
   More optimal solution would be using the Boyer-Moore algorithm. Initialize count to 0 and potential candidate to first element in array. Then increment or decrement count by iterating through the array and seeing if potential candidate is present or not. Once count reaches 0, change potential candidate to be present element. Return potential candidate left.

4. Contains Duplicate

   Leetcode
   Use hashmap to keep count of how many times an element appears while iterating through the array. If current element already in hashmap, return true. If loop concludes, return false as no duplicate elements.

5. Meeting Rooms

   Leetcode
   Premium leetcode required, didn't solve

6. Move Zeroes

   Leetcode
   Use 2 pointers starting from indices 0 and 1. 3 scenarios possible: both pointers = 0, move right one until find nonzero then swap; left pointer at 0 and right at nonzero, swap. left pointer at nonzero and right at zero, move both pointers 1 down array.

7. Squares of a Sorted Array

   Leetcode
   Yet to solve

8. Insert Interval

   Leetcode
   Create an array to store result. Iterate through intervals and check for 3 scenarios: if last num in new interval less than first num in curr element, append new interval and return result + rest of intervals; if first num in new interval greater than last num in curr element, append curr element; if none of the above, there is overlap thus update new interval numbers and continue iterating. at the end, append new interval and return res (if new interval was inserted, result would have been returned in first scenario).

9. 3Sum

   Leetcode
   Yet to solve

10. Product of Array Except Self

    Leetcode
    Initialize array to store results. Initialize prefix variable = 1. Start iterating through nums array and store the prefix in results array, then multiply prefix by current element before moving to next element. That way each index in the result array contains all numbers that came before that index in nums array multiplied. Repeat the same backwards with postfix that stores the suffix of numbers that came after the element. Return results array.

11. Combination Sum

    Leetcode
    Yet to solve

12. Merge Intervals

    Leetcode
    Yet to solve

13. Sort Colors

    Leetcode
    Yet to solve

14. Container With Most Water

    Leetcode
    Yet to solve

15. Gas Station

    Leetcode
    Yet to solve

16. Longest Consecutive Sequence

    Leetcode
    Yet to solve

17. Rotate Array

    Leetcode
    Yet to solve

18. Contiguous Array

    Leetcode
    Yet to solve

19. Subarray Sum Equals K

    Leetcode
    Yet to solve

20. Meeting Rooms II

    Leetcode
    Yet to solve

21. 3Sum Closest

    Leetcode
    Yet to solve

22. Non-overlapping Intervals

    Leetcode
    Yet to solve

23. Employee Free Time

    Leetcode
    Yet to solve

24. Sliding Window Maximum

    Leetcode
    Yet to solve

Stack

1. Valid Parentheses

   Leetcode
   Intialize hashmap matching all types of open brackets as keys to closing brackets as values. Then intialize stack adt using array, pushing opening brackets and only popping last one when you encounter a matching closing bracket. If array is empty, then all matching brackets are positioned in valid locations.

2. Implement Queue using Stacks

   Leetcode
   Yet to solve

3. Min Stack

   Leetcode
   Yet to solve

4. Backspace String Compare

   Leetcode
   Yet to solve

5. Evaluate Reverse Polish Notation

   Leetcode
   Yet to solve

6. Daily Temperatures

   Leetcode
   Yet to solve

7. Decode String

   Leetcode
   Yet to solve

8. Asteroid Collision

   Leetcode
   Yet to solve

9. Basic Calculator II

   Leetcode
   Yet to solve

10. Trapping Rain Water

    Leetcode
    Yet to solve

11. Basic Calculator

    Leetcode
    Yet to solve

12. Largest Rectangle in Histogram

    Leetcode
    Yet to solve

13. Maximum Frequency Stack

    Leetcode
    Yet to solve

14. Longest Valid Parentheses

    Leetcode
    Yet to solve

Linked List

1. Merge Two Sorted Lists

   Leetcode
   Initialize linkedlist called new and let a variable called prev point to it. Start while loop that checks if both lists 1 and 2 are not empty. 2 scenarios: val of curr node in list 1 less than that of 2 so let the next node of new be curr node of l1, and move to next node of l1; else, do the same for l2. Then set prev to next node of new and repeat. At end of loop, let prev.next equal to the non-empty list and return new.next as new.val is 0 and we started by changing new.next.

2. Linked List Cycle

   Leetcode
   Yet to solve

3. Reverse Linked List

   Leetcode
   Yet to solve

4. Middle of the Linked List

   Leetcode
   Yet to solve

5. Palindrome Linked List

   Leetcode
   Yet to solve

6. LRU Cache

   Leetcode
   Yet to solve

7. Remove Nth Node From End of List

   Leetcode
   Yet to solve

8. Swap Nodes in Pairs

   Leetcode
   Yet to solve

9. Odd Even Linked List

   Leetcode
   Yet to solve

10. Add Two Numbers

    Leetcode
    Yet to solve

11. Sort List

    Leetcode
    Yet to solve

12. Reorder List

    Leetcode
    Yet to solve

13. Rotate List

    Leetcode
    Yet to solve

14. Reverse Nodes in k-Group

    Leetcode
    Yet to solve

String

1. Valid Palindrome

   Leetcode
   Initalize start and end pointers on the array moving in opposite directions. If start and end pointing to alnum characters, check if they're equal (apply lowercase method) and return false if not else move pointers. If a pointer not pointing to alnum char, move the pointer. If loop finishes running, return true.

2. Valid Anagram

   Leetcode
   Initialize hash map to keep track of count of letters in first string, repeat for second string. Then iterate through both hash maps checking if a char is present in one and not the other or if count of characters in one not equal to count in other and return false. if all loops finish running, return true.

3. Longest Palindrome

   Leetcode
   Yet to solve

4. Longest Common Prefix

   Leetcode
   Yet to solve

5. Longest Substring Without Repeating Characters

   Leetcode
   Yet to solve

6. String to Integer (atoi)

   Leetcode
   Yet to solve

7. Longest Palindromic Substring

   Leetcode
   Yet to solve

8. Find All Anagrams in a String

   Leetcode
   Yet to solve

9. Group Anagrams

   Leetcode
   Yet to solve

10. Longest Repeating Character Replacement

    Leetcode
    Yet to solve

11. Largest Number

    Leetcode
    Yet to solve

12. Encode and Decode Strings

    Leetcode
    Yet to solve

13. Minimum Window Substring

    Leetcode
    Yet to solve

14. Palindrome Pairs

    Leetcode
    Yet to solve

Binary Tree

1. Invert Binary Tree

   Leetcode
   Yet to solve

2. Balanced Binary Tree

   Leetcode
   Yet to solve

3. Diameter of Binary Tree

   Leetcode
   Yet to solve

4. Maximum Depth of Binary Tree

   Leetcode
   Yet to solve

5. Same Tree

   Leetcode
   Yet to solve

6. Symmetric Tree

   Leetcode
   Yet to solve

7. Subtree of Another Tree

   Leetcode
   Yet to solve

8. Binary Tree Level Order Traversal

   Leetcode
   Yet to solve

9. Lowest Common Ancestor of a Binary Tree

   Leetcode
   Yet to solve

10. Binary Tree Right Side View

    Leetcode
    Yet to solve

11. Construct Binary Tree from Preorder and Inorder Traversal

    Leetcode
    Yet to solve

12. Path Sum II

    Leetcode
    Yet to solve

13. Maximum Width of Binary Tree

    Leetcode
    Yet to solve

14. Binary Tree Zigzag Level Order Traversal

    Leetcode
    Yet to solve

15. Path Sum III

    Leetcode
    Yet to solve

16. All Nodes Distance K in Binary Tree

    Leetcode
    Yet to solve

17. Serialize and Deserialize Binary Tree

    Leetcode
    Yet to solve

18. Binary Tree Maximum Path Sum

    Leetcode
    Yet to solve

Binary Search

1. Binary Search

   Leetcode
   Yet to solve

2. First Bad Version

   Leetcode
   Yet to solve

3. Search in Rotated Sorted Array

   Leetcode
   Yet to solve

4. Time Based Key-Value Store

   Leetcode
   Yet to solve

5. Search a 2D Matrix

   Leetcode
   Yet to solve

6. Find Minimum in Rotated Sorted Array

   Leetcode
   Yet to solve

7. Maximum Profit in Job Scheduling

   Leetcode
   Yet to solve

8. Median of Two Sorted Arrays

   Leetcode
   Yet to solve

Graph

1. Flood Fill

   Leetcode
   Yet to solve

2. 01 Matrix

   Leetcode
   Yet to solve

3. Clone Graph

   Leetcode
   Yet to solve

4. Course Schedule

   Leetcode
   Yet to solve

5. Number of Islands

   Leetcode
   Yet to solve

6. Rotting Oranges

   Leetcode
   Yet to solve

7. Accounts Merge

   Leetcode
   Yet to solve

8. Word Search

   Leetcode
   Yet to solve

9. Minimum Height Trees

   Leetcode
   Yet to solve

10. Pacific Atlantic Water Flow

    Leetcode
    Yet to solve

11. Shortest Path to Get Food

    Leetcode
    Yet to solve

12. Graph Valid Tree

    Leetcode
    Yet to solve

13. Course Schedule II

    Leetcode
    Yet to solve

14. Number of Connected Components in an Undirected Graph

    Leetcode
    Yet to solve

15. Minimum Knight Moves

    Leetcode
    Yet to solve

16. Cheapest Flights Within K Stops

    Leetcode
    Yet to solve

17. Word Ladder

    Leetcode
    Yet to solve

18. Longest Increasing Path in a Matrix

    Leetcode
    Yet to solve

19. Word Search II

    Leetcode
    Yet to solve

20. Alien Dictionary

    Leetcode
    Yet to solve

21. Bus Routes

    Leetcode
    Yet to solve

Dynamic Programming

1. Maximum Subarray

   Leetcode
   Yet to solve

2. Climbing Stairs

   Leetcode
   Yet to solve

3. Coin Change

   Leetcode
   Yet to solve

4. Partition Equal Subset Sum

   Leetcode
   Yet to solve

5. Unique Paths

   Leetcode
   Yet to solve

6. House Robber

   Leetcode
   Yet to solve

7. Maximum Product Subarray

   Leetcode
   Yet to solve

8. Longest Increasing Subsequence

   Leetcode
   Yet to solve

9. Jump Game

   Leetcode
   Yet to solve

10. Maximal Square

    Leetcode
    Yet to solve

11. Decode Ways

    Leetcode
    Yet to solve

12. Combination Sum IV

    Leetcode
    Yet to solve

Binary Search Tree

1. Lowest Common Ancestor of a Binary Search Tree

   Leetcode
   Yet to solve

2. Convert Sorted Array to Binary Search Tree

   Leetcode
   Yet to solve

3. Validate Binary Search Tree

   Leetcode
   Yet to solve

4. Kth Smallest Element in a BST

   Leetcode
   Yet to solve

5. Inorder Successor in BST

   Leetcode
   Yet to solve

Hash Table

1. Ransom Note

   Leetcode
   Yet to solve

2. Insert Delete GetRandom O(1)

   Leetcode
   Yet to solve

3. First Missing Positive

   Leetcode
   Yet to solve

Binary

1. Add Binary

   Leetcode
   Yet to solve

2. Counting Bits

   Leetcode
   Yet to solve

3. Number of 1 Bits

   Leetcode
   Yet to solve

4. Single Number

   Leetcode
   Yet to solve

5. Missing Number

   Leetcode
   Yet to solve

6. Reverse Bits

   Leetcode
   Yet to solve

7. Find the Duplicate Number

   Leetcode
   Yet to solve

Math

1. Roman to Integer

   Leetcode
   Yet to solve

2. Palindrome Number

   Leetcode
   Yet to solve

3. Random Pick with Weight

   Leetcode
   Yet to solve

4. Pow(x, n)

   Leetcode
   Yet to solve

5. Reverse Integer

   Leetcode
   Yet to solve

Heap

1. K Closest Points to Origin

   Leetcode
   Yet to solve

2. Task Scheduler

   Leetcode
   Yet to solve

3. Top K Frequent Words

   Leetcode
   Yet to solve

4. Find K Closest Elements

   Leetcode
   Yet to solve

5. Kth Largest Element in an Array

   Leetcode
   Yet to solve

6. Find Median from Data Stream

   Leetcode
   Yet to solve

7. Merge k Sorted Lists

   Leetcode
   Yet to solve

8. Smallest Range Covering Elements from K Lists

   Leetcode
   Yet to solve

Trie

1. Implement Trie (Prefix Tree)

   Leetcode
   Yet to solve

2. Word Break

   Leetcode
   Yet to solve

3. Design Add and Search Words Data Structure

   Leetcode
   Yet to solve

4. Design In-Memory File System

   Leetcode
   Yet to solve

Recursion

1. Permutations

   Leetcode
   Yet to solve

2. Subsets

   Leetcode
   Yet to solve

3. Letter Combinations of a Phone Number

   Leetcode
   Yet to solve

4. Next Permutation

   Leetcode
   Yet to solve

5. Generate Parentheses

   Leetcode
   Yet to solve

6. N-Queens

   Leetcode
   Yet to solve

Matrix

1. Spiral Matrix

   Leetcode
   Yet to solve

2. Valid Sudoku

   Leetcode
   Yet to solve

3. Rotate Image

   Leetcode
   Yet to solve

4. Set Matrix Zeroes

   Leetcode
   Yet to solve

5. Sudoku Solver

   Leetcode
   Yet to solve

Queue

1. Design Hit Counter

   Leetcode
   Yet to solve