An algorithm is a sequence of unambiguous steps to do a task. The challenges below require you to come up with algorithms to solve the problems.

Array
String
Dictionary
Dynamic Programming
Recursion
Tree

Reverse String
Kids with the Greatest Number of Candies
Max Consecutive Ones
Largest Number At Least Twice of Others
Third Maximum Number
Plus One
Check If It Is a Straight Line
How Many Numbers Are Smaller Than the Current Number
Replace Elements with Greatest Element on Right Side
Find Pivot Index
Best Time to Buy and Sell Stock
Can Place Flowers
Monotonic Array
Valid Mountain Array
Best Time to Buy and Sell Stock II
Maximum Subarray
Image Smoother
Shift 2D Grid

Valid Palindrome
Student Attendance Record I
Detect Capital
Valid Parentheses
Goat Latin
Implement strStr()
Positions of Large Groups
Longest Common Prefix
Long Pressed Name
Valid Palindrome II
Longest Palindromic Substring
Camelcase Matching

Contains Duplicate
First Unique Character in a String
Majority Element
Jewels and Stones
Find Lucky Integer in an Array
Check If N and Its Double Exist
Two Sum
Intersection of Two Arrays
Minimum Index Sum of Two Lists
Find the Difference
Uncommon Words from Two Sentences
Isomorphic Strings
Pairs of Songs with Total Durations Divisible by 60
Fair Candy Swap
Set Mismatch
Keyboard Row
Ransom Note
Maximum Number of Balloons
Roman to Integer
Find the Town Judge
Valid Anagram
Find Words That Can Be Formed by Characters
Find Common Characters
Shortest Completing Word
Longest Substring Without Repeating Characters
Group Anagrams
Top K Frequent Elements
Valid Sudoku
Alphabet Board Path
Task Scheduler

Fibonacci Number
Pascal's Triangle
Climbing Stairs
Min Cost Climbing Stairs
House Robber
Divisor Game
Unique Paths
Minimum Path Sum
Coin Change
Longest Increasing Subsequence
Decode Ways
2 Keys Keyboard

Number of Steps to Reduce a Number to Zero
Power of Three
Add Digits
Happy Number
Last Stone Weight
Count and Say
Pow(x, n)
K-th Symbol in Grammar
Jump Game
Keys and Rooms
Number of Islands
Number of Provinces
Word Search
Time Needed to Inform All Employees
Subsets
Combinations
Rotting Oranges
Target Sum
Letter Combinations of a Phone Number
Permutations
Perfect Squares
Maximal Square
Open the Lock
Generate Parentheses

Binary Tree Preorder Traversal
Binary Tree Inorder Traversal
Binary Tree Postorder Traversal
Binary Tree Level Order Traversal
Same Tree
Univalued Binary Tree
Maximum Depth of Binary Tree
Path Sum
Sum of Left Leaves
Binary Tree Paths
Merge Two Binary Trees
Symmetric Tree