HackerRank Problems

Solutions for the practice problems on HackerRank.

C++ / Python / PHP

Strings

Attribute Parser :: [C++ STL] {medium}

• string input via cin
• string.substr
• string.find_first_of
• vector<string>
• unordered_map<string, string>

The Minion Game :: [Python] {medium}

• substrings
• Counter class (in Version 1)

Merge the Tools! :: [Python] {medium}

• substrings

ginortS :: [Python] {medium}

• sorted with key

Classes

Exceptional Server :: [C++ STL] {medium}

• throw with try-catch
• standard and non-standard exceptions

Inherited Code :: [C++ STL] {medium}

• custom exceptions with parameters

Virtual Functions :: [C++ STL] {medium}

• abstract functions
• virtual functions
• overloaded functions
• static fields

Abstract Classes - Polymorphism :: [C++ STL] {hard}

• abstract functions
• virtual functions
• double-linked lists
• map

Accessing Inherited Functions :: [C++ STL] {medium}

• multiple inheritance
• private, protected, and public functions

Operator Overloading :: [C++ STL] {medium}

• operator overloading
• 2-D vector

Messages Order :: [C++ STL] {medium}

• static fields
• operator overloading

Template Specialization :: [C++ STL] {medium}

• enum
• class/struct template specialization

Variadics :: [C++ STL] {hard}

• template parameter packs
• variadic templates
• non-type template parameters

Magic Spells :: [C++ STL] {hard}

• dynamic_cast
• 2-D vector
• Longest common subsequence problem

Algorithms / Data Structures / Containers

Quicksort 1 - Partition :: [C++ STL] [PHP] {easy}

• Quicksort

No Idea! :: [Python] {medium}

• sets

Count Triplets :: [Python] {medium}

• hash table
• tuples

Deque :: [C++ STL] {medium}

• deque<int>

Piling Up! :: [Python] {medium}

• collection.deque

DefaultDict Tutorial :: [Python] {easy}

• collections.defaultdict

Hash Tables: Ransom Note :: [Python] {medium}

• collectios.Counter

Binary Search Tree : Lowest Common Ancestor :: [C++ STL] {easy}

• Binary Search Tree

Is This a Binary Search Tree? :: [C++ STL] {medium}

• Binary Search Tree

Tree: Level Order Traversal :: [C++ STL] {easy}

• Binary Tree

Attending Workshops :: [C++ STL] {medium}

• Interval scheduling maximization problem
• initializing an array of unknown size
• vector sort with a custom function

Bit Array :: [C++ STL] {hard}

• bit operations
• Set bits in an integer / Brian Kernighan's Algorithm

Construct the Array :: [C++ STL] {medium}

• construct an array with n elements such that each element between 1 and k, inclusive
• the first and last elements of the array to be 1 and x

Array Manipulation :: [C++ STL] {hard}

• Difference Array | Range update query in O(1)

QHEAP1 :: [C++ STL] [Python] {easy}

• heap<int> (C++) / heapq (Python)

Extra Long Factorials :: [C++ STL] {medium}

• big integers
• vector.reverse_iterator

Roads and Libraries :: [C++ STL] {medium}

• graphs
• depth first search
• connected components

Python

Easy problems (in one Jupyter Notebook) :: [Python]

Medium and Hard problems (in individual files) :: [Python]

Itertools

Iterables and Iterators :: [Python] {medium}

• itertools.permutations

Compress the String! :: [Python] {medium}

• itertools.groupby
• list comprehension

Maximize It! :: [Python] {hard}

• itertools.product
• map
• list comprehension

SQL

Basic Select

Weather Observation Station 4 :: [SQL] {easy}

• count / distinct count

Weather Observation Station 5 :: [SQL] {easy}

• shortest / longest string value in the table

Weather Observation Station 8 :: [SQL] {easy}

• starting or ending with a vowel

Weather Observation Station 11 :: [SQL] {easy}

• not starting or not ending with a vowel

Basic Join

The Report :: [SQL]

• inner join, case

Top Competitors :: [SQL]

• inner join, group by, having, count

Ollivander's Inventory :: [SQL]

• inner join, min

Challenges :: [SQL]

• inner join, group by, having, count

Contest Leaderboard :: [SQL]

• inner join, group by, having, sum, max

Aggregation

Weather Observation Station 18 :: [SQL] {medium}

• Manhattan distance
• cast, max, min, abs

Weather Observation Station 19 :: [SQL] {medium}

• Euclidean distance
• cast, max, min, square, sqrt

Weather Observation Station 20 :: [SQL] {medium}

• Median value in a table

The Blunder :: [SQL] {easy}

• cast, avg, replace, ceiling

Alternative Queries

Draw The Triangle 1 :: [SQL]

• Version 1: while, replicate
• Version 2: Recursive Common Table Expressions (CTE's)

Print Prime Numbers :: [SQL]

• Control of Flow: while, break, if

Advanced Select

Not A Triangle :: [SQL] {easy}

• case

The PADS :: [SQL] {medium}

• group by, count, left, lower, cast

Occupations :: [SQL] {medium}

• rank, partition, pivot

Binary Tree Nodes :: [SQL] {medium}

• case, exists

New Companies :: [SQL] {medium}

• join, count distinct, group by

Advanced Join

15 Days of Learning SQL :: [SQL] {hard}

• with, row_number over, partition by, group by, count, datediff
• Common Table Expressions (CTE's)

Projects :: [SQL] {medium}

• Finding Sequences Tabibitosan Method
• cross join (Cartesian Product)
• with, row_number over, datediff

Placements :: [SQL] {medium}

• join

Symmetric Pairs :: [SQL] {medium}

• with, row_number over
• Common Table Expressions (CTE's)

Linux Shell

[bash]