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Two sum problem

A popular interview question that requires you to determine if two numbers in an array sum to a specific value. A solution can be written that runs in linear time.
Print the power set of a given set

Solution for printing all possible subsets of a given set.
Find all string combinations of only 0, 1 and ?

Print all possible strings of 0's and 1's where the ? is a wildcard.
Find all duplicates in an array (version 1)

Solution for finding all duplicates in an array where the elements range from 1 to n-1.
Find all duplicates in an array (version 2)

A common interview question where your goal is to find all duplicates in an array in linear time.
Stock maximum profit

Solution that explains how to calculate the maxiumum profit that could be made in a list of stock prices.
Challenges
Consecutive

For this challenge you will determine how to order an array of numbers consecutively.

6229 solutions

Solution
Permutation Step

For this challenge you will determine the next greatest number using the same numbers of a given argument.

8254 solutions

Solution
K Unique Characters

For this challenge you will be searching a string for a particular substring.

3935 solutions

Solution
Bitmap Holes

For this challenge you will be searching within a 2D matrix.

3086 solutions

Solution
Pattern Chaser

For this challenge you will be given a string and you will have to determine whether some sort of pattern exists.

2198 solutions

Solution
Gas Station

For this challenge you will be determining whether a car can get around a route with a limited amount of gas.

2707 solutions

Solution
Square Figures

For this challenge you will be determining squares of certain numbers.

375 solutions

Solution
Array Jumping

For this challenge you will determine how many times you can jump around within an array.

1000 solutions

Solution
Parallel Sums

For this challenge you will determine how to properly split an array into two sets.

1479 solutions

Solution
Simple SAT

This challenge will require knowledge of basic Boolean logic.

312 solutions

Solution
Counting Anagrams

For this challenge you will determine how many anagrams exist in a string.

2231 solutions

Solution
Array Rotation

This challenge will require knowledge of arrays.

2023 solutions

Solution
Maximal Rectangle

For this challenge you will be searching a matrix for the largest rectangle submatrix.

682 solutions

Solution

Sorting
Dutch national flag sorting problem

Question and solution for sorting an array of 0's, 1's, and 2's in place and in linear time.
Implement bubble sort

Code for implementing the simple but slow sorting algorithm, bubble sort.
Insert an interval into a list of sorted disjoint intervals

Solution for inserting an interval into an already sorted list of disjoint intervals.
Challenges
Alphabet Soup

For this challenge you will be sorting characters in a string.

51604 solutions

Solution
Wave Sorting

For this challenge you will determine if numbers in an array can be sorted in a particular way.

4153 solutions

Solution
Switch Sort

For this challenge you will determine how quickly you can sort an array based on a specific sorting technique.

2296 solutions

Solution

Dynamic Programming
Subset sum problem

Important computer science question where the goal is to find a subset that sums to some number.
Challenges
Array Addition I

For this challenge you will determine if numbers in an array can add up to a certain number in the array.

11400 solutions

Solution
Array Addition

For this challenge you will determine if numbers in an array can add up to a certain number in the array.

8899 solutions

Solution
LCS

For this challenge you will be determining the longest common subsequence of two strings.

732 solutions

Solution
Maximal Square

For this challenge you will be searching a matrix for the largest square submatrix.

5630 solutions

Solution

Stacks and Queues
Implement a queue using a linked list

Solution for how to implement a queue using a linked list data structure.
Implement a queue using two stacks

Solution for how to implement a queue using the stack data structure.
Challenges
Reverse Polish Notation

This challenge will require knowledge of postfix notation for arithmetic expressions.

1308 solutions

Solution