Connected Components in an Undirected Graph [Solution]

Connected Components in an Undirected Graph

Given an undirected graph represented as an adjacency list, implement a function to find the number of connected components in the graph.

Count Bits [Solution]

Count Bits

Given a non-negative integer num, create an array result of length num + 1 where each element result[i] represents the number of 1’s in the binary representation of i.

Missing Positive [Solution]

Missing Positive

Given an unsorted integer array, find the smallest missing positive integer.

Binary Tree Path Sum [Solution]

Binary Tree Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Bitonic Array Maximum [Solution]

Bitonic Array Maximum

A bitonic array is an array that starts strictly increasing and then strictly decreasing. Given a bitonic array arr of distinct integers, find the maximum element in the array. You may assume that the array always contains at least one element.

Inorder Successor in Binary Search Tree [Solution]

Inorder Successor in Binary Search Tree

Given a binary search tree (BST) and a node p in it, find the in-order successor of that node in the BST.

Maximum Subarray Sum [Solution]

Maximum Subarray Sum

Given an array of integers, find the contiguous subarray (containing at least one number) that has the largest sum and return its sum.

Course Schedule [Solution]

Course Schedule

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [y, x] indicates that you must take course x first if you want to take course y.

Longest Increasing Subsequence [Solution]

Longest Increasing Subsequence

Given an unsorted array of integers, find the length of the longest increasing subsequence (LIS).

Search in Rotated Sorted Array [Solution]

Search in Rotated Sorted Array

Suppose an array of length n sorted in ascending order is rotated between 1 and n times. Given a target value target, write a function to search for the target in the rotated sorted array.

Lowest Common Ancestor in Binary Tree [Solution]

Lowest Common Ancestor in Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes p and q in the tree.

Symmetric Binary Tree [Solution]

Symmetric Binary Tree

Given a binary tree, check whether it is a symmetric tree. A symmetric tree is a mirror image of itself with respect to its center.

Longest Palindromic Substring [Solution]

Longest Palindromic Substring

Given a string, find the longest palindromic substring in it. A palindrome is a word, phrase, or sequence that reads the same backward as forward. A substring is a contiguous sequence of characters within the string.

Longest Common Prefix [Solution]

Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

Rotate Image [Solution]

Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

Median of Two Sorted Arrays [Solution]

Median of Two Sorted Arrays

You are given two sorted arrays, nums1 and nums2, where nums1 has size m and nums2 has size n. Your task is to find the median of the two sorted arrays. If possible, the overall run time complexity should be O(log(min(m, n))).

Word Search 2 [Solution]

Word Search 2

Given a 2D board of characters and a list of words, find all words in the board.

Minimize Meeting Rooms [Solution]

Minimize Meeting Rooms

Given a list of meetings with start and end times, determine the minimum number of meeting rooms required to accommodate all the meetings. The start and end times of the meetings are represented as tuples (start_time, end_time).

Minimum Cost to Climb Stairs [Solution]

Minimum Cost to Climb Stairs

You are given an array cost where cost[i] is the cost of i-th step on a staircase. You can start from either the 0-th step or the 1-st step. Each step can be climbed by paying the cost specified, and you can either climb one step or two steps at a time.

Longest Substring with K Distinct Characters [Solution]

Longest Substring with K Distinct Characters

Given a string s and an integer k, find the length of the longest substring with at most k distinct characters.

Reverse a Linked List [Solution]

Reverse a Linked List

You are given a singly linked list. Write a function to reverse the linked list.

Product of Array Except Self [Solution]

Product of Array Except Self

Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Coin Change [Solution]

Coin Change

Given a set of coin denominations and a target amount, determine the minimum number of coins needed to make up that amount.

Kth Largest Element in an Array [Solution]

Kth Largest Element in an Array

Given an integer array nums and an integer k, return the kth largest element in the array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Word Search [Solution]

Word Search

Given a 2D board of letters and a word, determine if the word exists in the grid.

Valid Parentheses [Solution]

Valid Parentheses

Given a string containing just the characters (, ), {, }, [ and ], determine if the input string is valid.

Merge Overlapping Intervals [Solution]

Merge Overlapping Intervals

Given a list of intervals, where each interval is represented as a pair of integers [start, end], write a function to merge overlapping intervals.

Minimum Window Substring [Solution]

Minimum Window Substring

Given a string s and a string t, find the minimum window in s that contains all the characters of t in any order. If there is no such window, return an empty string “”.

Two Sum [Solution]

Two Sum

Given an array of integers nums and an integer target, return the indices of the two numbers such that they add up to the target.

Subarray Product Less Than K [Solution]

Subarray Product Less Than K

Given an array of positive integers and an integer k, find the number of contiguous subarrays where the product of all the elements is less than k.

Design a Doubly Linked List [Solution]

Design a Doubly Linked List

Design a doubly linked list (DLL) with the following operations:

1. insert_at_head(val): Insert a node with the given value at the beginning of the doubly linked list.
2. insert_at_tail(val): Insert a node with the given value at the end of the doubly linked list.
3. insert_after_node(node, val): Insert a node with the given value after the specified node in the doubly linked list.
4. delete_at_head(): Delete the node at the beginning of the doubly linked list.
5. delete_at_tail(): Delete the node at the end of the doubly linked list.
6. delete_node(node): Delete the specified node from the doubly linked list.
7. display(): Display the elements of the doubly linked list.

Word Break [Solution]

Word Break

Given a non-empty string and a dictionary containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

Kth Smallest Element in a Sorted Matrix [Solution]

Kth Smallest Element in a Sorted Matrix

Given an n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.

Maximum Depth of Binary Tree [Solution]

Maximum Depth of Binary Tree

Given the root of a binary tree, find its maximum depth.

Two Sum Less Than K [Solution]

Two Sum Less Than K

Given an array nums of integers and an integer k, find two distinct indices i and j in the array such that nums[i] + nums[j] is the maximum possible value less than k. If no such indices exist, return -1.

Container With Most Water [Solution]

Container With Most Water

Given n non-negative integers a1, a2, ..., an, where each represents a point at coordinate (i, ai), n vertical lines are drawn such that the two endpoints of the line i are at (i, ai) and (i, 0). Find two lines, which, together with the x-axis, forms a container that would hold the greatest amount of water. Return the maximum area of the water it can contain.

Perfect Squares Sum [Solution]

Perfect Squares Sum

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, …) that sum up to n.

Anagram Groups [Solution]

Anagram Groups

Given a list of strings, write a function to group the strings into sets of anagrams.

Sum of Left Leaves in Binary Tree [Solution]

Sum of Left Leaves in Binary Tree

Given the root of a binary tree, return the sum of all left leaves.

Binary Tree Maximum Path Sum [Solution]

Binary Tree Maximum Path Sum

Given a binary tree, find the maximum path sum. The path may start and end at any node in the tree.

Valid Sudoku [Solution]

Valid Sudoku

Determine whether a 9 x 9 Sudoku board is valid.

Longest Consecutive Sequence in an Array [Solution]

Longest Consecutive Sequence in an Array

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Kth Smallest Element in a Binary Search Tree [Solution]

Kth Smallest Element in a Binary Search Tree

Given a binary search tree (BST), find the kth smallest element in it.

Invert Binary Tree [Solution]

Invert Binary Tree

Given the root of a binary tree, invert the tree by swapping the left and right children of each node.

Find the Missing Number [Solution]

Find the Missing Number

You are given an array of length n containing n distinct numbers taken from the range 0 to n. Since the array has n distinct numbers and the numbers are in the range 0 to n, there is exactly one number missing.

Sum of Digits Until a Single Digit [Solution]

Sum of Digits Until a Single Digit

Given a non-negative integer, repeatedly add all its digits until the result has only one digit.

Unique Paths [Solution]

Unique Paths

A robot is located at the top-left corner of a m x n grid. The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid. How many possible unique paths are there?

Minimum Cost to Reach Destination in a Weighted Graph [Solution]

Minimum Cost to Reach Destination in a Weighted Graph

You are given a weighted graph represented by an adjacency matrix graph where graph[i][j] represents the cost to move from node i to node j. Each node is labeled from 0 to n-1. You are also given two nodes source and destination.

Word Ladder Transformation [Solution]

Word Ladder Transformation

Given two words, beginWord and endWord, and a dictionary of words wordList, find the length of the shortest transformation sequence from beginWord to endWord such that:

Binary Tree Level Order Traversal [Solution]

Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes’ values. Level order traversal means traversing the tree level by level, from left to right.

Merge Sorted Arrays [Solution]

Merge Sorted Arrays

You are given an array of k sorted integer arrays, where each array is sorted in ascending order. Merge these arrays into a single sorted array.

Merge K Sorted Linked Lists [Solution]

Merge K Sorted Linked Lists

Merge k sorted linked lists and return it as one sorted list.

Shortest Path in Binary Matrix [Solution]

Shortest Path in Binary Matrix

Given a binary matrix representing an obstacle grid where 0 represents an empty cell and 1 represents an obstacle, find the length of the shortest path from the top-left corner (0, 0) to the bottom-right corner (m-1, n-1). If there is no path, return -1.

Rotate Array to the Right [Solution]

Rotate Array to the Right

Given an array, rotate the array to the right by k steps, where k is a non-negative integer. The function should modify the input array in-place.

Find All Anagrams in a String [Solution]

Find All Anagrams in a String

Given a string s and a non-empty string p, find all the start indices of p’s anagrams in s.

Reverse Linked List [Solution]

Reverse Linked List

Given the head of a singly linked list, reverse the list without modifing the values of the nodes (modify only their pointers).

Longest Substring Without Repeating Characters [Solution]

Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Rearrange Array Elements [Solution]

Rearrange Array Elements

Given an array of positive integers, rearrange the elements such that the resulting number formed by concatenating the elements is the largest possible number.

Palindromic Substrings [Solution]

Palindromic Substrings

Given a string s, return the number of palindromic substrings in it.

String Power [Solution]

String Power

Given a string s, the power of the string is the maximum length of a non-empty substring that contains only one unique character.

Spiral Matrix [Solution]

Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Integer Hamming Distance [Solution]

Integer Hamming Distance

The Hamming distance between two integers is the number of positions at which the corresponding bits are different. Given two integers x and y, calculate the Hamming distance between them.

Reverse Bits [Solution]

Reverse Bits

Given an unsigned integer, reverse its binary representation (i.e., reading it from right to left).

Maximum Product Subarray [Solution]

Maximum Product Subarray

Given an integer array, find the contiguous subarray within the array (containing at least one number) that has the largest product. Return the maximum product.

Maximum XOR Pair [Solution]

Maximum XOR Pair

Given an array of integers, find the maximum XOR value between any two elements in the array.

Randomized Shuffle [Solution]

Randomized Shuffle

Given an array of integers, implement a function to shuffle the array randomly. Each permutation of the array should be equally likely.

Linked List Cycle [Solution]

Linked List Cycle

Given a linked list, determine if it has a cycle in it. A cycle is defined as having at least one node in the list whose next is the node itself.

Subarray Sum Equals K [Solution]

Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.

Letter Combinations of a Phone Number [Solution]

Letter Combinations of a Phone Number

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Three Sum [Solution]

Three Sum

Given an array nums of n integers, find all unique triplets in the array which gives the sum of zero.

Reverse Words [Solution]

Reverse Words

Given a string containing words separated by spaces, reverse the order of words in the string. For example, given the input string "Hello World", the output should be "World Hello".

Buy and Sell Stock [Solution]

Buy and Sell Stock

You are given an array prices where prices[i] is the price of a given stock on the ith day.

Find Peak Element [Solution]

Find Peak Element

A peak element in an array is an element that is greater than or equal to its neighbors. Given an input array nums where nums[i] != nums[i+1], find a peak element and return its index.

Anagram Pairs [Solution]

Anagram Pairs

Given an array of strings, find the number of pairs of strings that are anagrams of each other. Two strings are considered anagrams if they have the same characters, but in a different order.

Valid Palindrome [Solution]

Valid Palindrome

Given a string, determine if it is a palindrome. A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward, ignoring spaces, punctuation, and capitalization.