Tech Interview problems, solutions and explanations

Summary

A collection of LeetCode solutions to practice various programming languages, mainly java python sometimes ruby kotlin

Problem set

(Part of Top 150)

Approach

Follow each problem link to to see its description, solution and explanation. The solution may appear in multiple languages, just for fun.

Problem category

Array / String

Array	Difficulty	Tag
Kids with the Greatest Number of Candies		LC75
Can Place Flowers		LC75
Merge Sorted Array	*	Top150
Majority Element	*	Top150
Remove Element		Top150
Remove Duplicates from Sorted Array I		Top150
Remove Duplicates from Sorted Array II		Top150
Product of Array Except Self		LC75
Increasing Triplet Subsequence		LC75
Candy		Top150
Trapping Rain Water		Top150

String	Difficulty	Tag
Merge Strings Alternately		LC75
Greatest Common Divisor of Strings	*	LC75
Reverse Vowels of a String		LC75
Roman to Integer		Top150
Integer to Roman		Top150
Reverse Words in a String		LC75
String Compression		LC75

Two Pointers

Two Pointers	Difficulty	Tag
Move Zeroes		LC75
Is Subsequence		LC75
Container With Most Water		LC75
Max Number of K-sum Pairs		LC75

Sliding Window

Sliding Window	Difficulty	Tag
Maximum Average Subarray I		LC75
Maximum Number Of Vowels In A Substring Of Given Length		LC75
Max Consecutive Ones III		LC75
Longest Subarray of 1's After Deleting One Element		LC75

Prefix Sum

Prefix Sum	Difficulty	Tag
Find the Highest Altitude		LC75
Find Pivot Index		LC75

Hashmap / Set

Hashmap / Set	Difficulty	Tag
Find the Difference of Two Arrays		LC75
Unique Number Of Occurrences		LC75
Determine If Two Strings Are Close		LC75
Equal Row and Column Pairs		LC75

Stack

Stack	Difficulty	Tag
Removing Stars from a String	*	LC75
Asteroid Collision		LC75
Decode String		LC75

Queue

Queue	Difficulty	Tag
Number of Recent Calls		LC75
Dota2 Senate		LC75

Linked List

Linked List	Difficulty	Tag
Reverse Linked List		LC75
Delete The middle Node of a Linked List		LC75
Odd Even Linked List		LC75
Maximum Twin Sum of a Linked List		LC75

Binary Tree

Depth-First Search (DFS)	Difficulty	Tag
Maximum Depth of Binary Tree		LC75
Leaf-similar Trees		LC75
Count Good Nodes in Binary Tree		LC75
Path Sum III	*	LC75
Longest ZigZag Path in a Binary Tree		LC75
Lowest Common Ancestor of a Binary Tree		LC75

Breadth-First Search (BFS)	Difficulty	Tag
Binary Tree Right Side View		LC75
Maximum Level Sum of a Binary Tree		LC75

Binary Search (BST)	Difficulty	Tag
Search in a Binary Search Tree		LC75
Delete Node in a BST		LC75

Graphs

Depth-First Search (DFS)	Difficulty	Tag
Keys and Rooms		LC75
Number of Provinces		LC75
Reorder Routes to Make All Paths Lead to the City Zero		LC75
Evaluate Division		LC75
Spreadsheet		Real Interview

Breadth-First Search (BFS)	Difficulty	Tag
Nearest Exit from Entrance in Maze		LC75
Rotting Oranges		LC75
Crawler		Real Interview

Heap / Priority Queue

Heap / Priority Queue	Difficulty	Tag
Kth Largest Element in an Array		LC75
Smallest Number in Infinite Set		LC75
Maximum Subsequence Score	*	LC75
Total Cost to Hire K Workers		LC75

Binary Search

Binary Search	Difficulty	Tag
Guess Number Higher or Lower		LC75
Successful Pairs of Spells or Potions		LC75
Find Peak Element		LC75
Koko Eating Bananas		LC75

Backtracking

Backtracking	Difficulty	Tag
Letter Combinations of a Phone Number		LC75
Combination Sum III		LC75

Dynamic Programming

1 Dimensional	Difficulty	Tag
Nth Tribonacci Number		LC75
Min Cost Climbing Stairs		LC75
House Robber		LC75
Domino and Tromino Tiling		LC75

Multi Dimensional	Difficulty	Tag
Unique Paths		LC75
Longest Common Subsequence		LC75
Best Time to Buy and Sell Stock with Transaction Fee	*	LC75
Edit Distance		LC75

Bit Manipulation

Bit Manipulation	Difficulty	Tag
Counting Bits		LC75
Single Number		LC75
Minimum Flips to Make a OR b Equal to c		LC75

Trie

Trie	Difficulty	Tag
Implement Trie (Prefix Tree)		LC75
Search Suggestions System		LC75

Intervals

Intervals	Difficulty	Tag
Non-overlapping Intervals		LC75
Minimum Number of Arrows to Burst Balloons		LC75

Monotonic Stack

Monotonic Stack	Difficulty	Tag
Daily Temperatures		LC75
Online Stock Span		LC75

Hard / Misc

LeetCode Hard	Difficulty
Count of Numbers After Self
Longest Consecutive Sequence
Minimum Window Substring
Skyline
Sliding Window Maximum
Sum Divisibles
Wildcard Matching

Legend

You will find these badges on top of each problem page:

* Asterisk indicates disputed difficulty.