Yahoo Coding Interview Questions

Two Sum

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

Longest Substring Without Repeating Characters

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

Container With Most Water

You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i, 0) and (i, height[i]).

Roman to Integer

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Maximum Depth of Binary Tree

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

3Sum

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

Median of Two Sorted Arrays

Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.

Remove Duplicates from Sorted Array

Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order o...

Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a sing...

Merge Sorted Array

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num...

LRU Cache

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.

Longest Palindromic Substring

Given a string s, return the longest palindromic substring in s.

Word Break

Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.

Best Time to Buy and Sell Stock

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

Rotate Image

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

Valid Parentheses

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

Linked List Cycle

Given head, the head of a linked list, determine if the linked list has a cycle in it.

Climbing Stairs

You are climbing a staircase. It takes n steps to reach the top.

Palindrome Number

Given an integer x, return true if x is a palindrome, and false otherwise.

Merge Two Sorted Lists

You are given the heads of two sorted linked lists list1 and list2.

Longest Common Prefix

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

Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Merge Intervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cove...

Jump Game

You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length...

Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order.

Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

Remove Element

Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number...

Search Insert Position

Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were ins...

Group Anagrams

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

Combination Sum

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum...

Count and Say

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

Reverse Integer

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1...

Plus One

You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most sig...

Find First and Last Position of Element in Sorted Array

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

Find the Index of the First Occurrence in a String

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Subsets

Given an integer array nums of unique elements, return all possible subsets (the power set).

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. Return the answer in any order.

Divide Two Integers

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator.

Maximum Subarray

Given an integer array nums, find the subarray with the largest sum, and return its sum.

Set Matrix Zeroes

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0's.

Sqrt(x)

Given a non-negative integer x, return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well.

Pascal's Triangle

Given an integer numRows, return the first numRows of Pascal's triangle.

Pow(x, n)

Implement pow(x, n), which calculates x raised to the power n (i.e., xn).

Valid Palindrome

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forwa...

Next Permutation

A permutation of an array of integers is an arrangement of its members into a sequence or linear order.

Binary Tree Level Order Traversal

Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).

Regular Expression Matching

Given an input string s and a pattern p, implement regular expression matching with support for '.' and '' where:

Largest Rectangle in Histogram

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the his...

Zigzag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better...

Validate Binary Search Tree

Given the root of a binary tree, determine if it is a valid binary search tree (BST).

Single Number

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

Search a 2D Matrix

You are given an m x n integer matrix matrix with the following two properties:

Recover Binary Search Tree

You are given the root of a binary search tree (BST), where the values of exactly two nodes of the tree were swapped by mistake. Recover the tree without changi...

Longest Consecutive Sequence

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

Search in Rotated Sorted Array

There is an integer array nums sorted in ascending order (with distinct values).

Length of Last Word

Given a string s consisting of words and spaces, return the length of the last word in the string.

Gas Station

There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i].

3Sum Closest

Given an integer array nums of length n and an integer target, find three integers at distinct indices in nums such that the sum is closest to target.

Permutations

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Sort Colors

Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order...

Binary Tree Preorder Traversal

Given the root of a binary tree, return the preorder traversal of its nodes' values.

Unique Paths

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner...

Integer to Roman

Seven different symbols represent Roman numerals with the following values:

Remove Duplicates from Sorted Array II

Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative or...

Valid Sudoku

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

String to Integer (atoi)

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.

4Sum

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

Remove Nth Node From End of List

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Symmetric Tree

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

Best Time to Buy and Sell Stock II

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

Maximum Product Subarray

Given an integer array nums, find a subarray that has the largest product, and return the product.

N-Queens

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Simplify Path

You are given an absolute path for a Unix-style file system, which always begins with a slash '/'. Your task is to transform this absolute path into its simplif...

Same Tree

Given the roots of two binary trees p and q, write a function to check if they are the same or not.

Unique Paths II

You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-r...

Unique Binary Search Trees

Given an integer n, return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n.

Maximal Rectangle

Given a rows x cols binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.

Palindrome Partitioning

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.

Insert Interval

You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and interv...

Longest Valid Parentheses

Given a string containing just the characters '(' and ')', return the length of the longest valid (well-formed) parentheses substring.

Minimum Path Sum

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path.

Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc...

Interleaving String

Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2.

Flatten Binary Tree to Linked List

Given the root of a binary tree, flatten the tree into a "linked list":

Reverse Linked List II

Given the head of a singly linked list and two integers left and right where left <= right, reverse the nodes of the list from position left to position right,...

Reverse Nodes in k-Group

Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.

Edit Distance

Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2.

Reorder List

You are given the head of a singly linked-list. The list can be represented as:

Merge k Sorted Lists

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.

Construct Binary Tree from Preorder and Inorder Traversal

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, c...

Single Number II

Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element and return it.

Word Ladder

A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:

Sort List

Given the head of a linked list, return the list after sorting it in ascending order.

Find Minimum in Rotated Sorted Array

Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example, the array nums = [0,1,2,4,5,6,7] might become:

Copy List with Random Pointer

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Clone Graph

Given a reference of a node in a connected undirected graph.

Pascal's Triangle II

Given an integer rowIndex, return the rowIndexth (0-indexed) row of the Pascal's triangle.

Rotate List

Given the head of a linked list, rotate the list to the right by k places.

Search in Rotated Sorted Array II

There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values).