Uber 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.

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.

Word Search

Given an m x n grid of characters board and a string word, return true if word exists in the grid.

Text Justification

Given an array of strings words and a width maxWidth, format the text such that each line has exactly maxWidth characters and is fully (left and right) justifie...

Spiral Matrix

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

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:

Group Anagrams

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

Roman to Integer

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

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.

Generate Parentheses

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

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...

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...

Longest Common Prefix

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

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.

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.

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...

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...

Rotate Image

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

Search in Rotated Sorted Array

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

Decode Ways

You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping:

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.

Next Permutation

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

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...

Maximum Depth of Binary Tree

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

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.

Valid Parentheses

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

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.

Merge Two Sorted Lists

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

Regular Expression Matching

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

Longest Consecutive Sequence

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

Merge k Sorted Lists

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

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...

Word Break II

Given a string s and a dictionary of strings wordDict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possi...

Maximum Subarray

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

Subsets

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

Sudoku Solver

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

Longest Palindromic Substring

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

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...

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...

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.

String to Integer (atoi)

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

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only...

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...

Clone Graph

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

Longest Substring Without Repeating Characters

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

Jump Game II

You are given a 0-indexed array of integers nums of length n. You are initially positioned at index 0.

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.

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]).

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.

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...

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:

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...

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...

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...

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...

Longest Valid Parentheses

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

Candy

There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings.

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.

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).

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.

Length of Last Word

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

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.

Divide Two Integers

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

First Missing Positive

Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums.

Pascal's Triangle

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

Linked List Cycle

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

Permutations

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

Combination Sum II

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to...

Add Binary

Given two binary strings a and b, return their sum as a binary string.

Binary Tree Maximum Path Sum

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequ...

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.

Validate Binary Search Tree

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

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.

Search in Rotated Sorted Array II

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

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:

Binary Tree Inorder Traversal

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

Flatten Binary Tree to Linked List

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

Interleaving String

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

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...

Pow(x, n)

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

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.

Distinct Subsequences

Given two strings s and t, return the number of distinct subsequences of s which equals t.

Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

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...

Unique Binary Search Trees II

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

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...

Spiral Matrix II

Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order.

Convert Sorted List to Binary Search Tree

Given the head of a singly linked list where elements are sorted in ascending order, convert it to a height-balanced binary search tree.

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.

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.

Multiply Strings

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Wildcard Matching

Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '' where:

Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

Integer to Roman

Seven different symbols represent Roman numerals with the following values:

Best Time to Buy and Sell Stock III

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

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,...

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...