Apple 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.

Longest Common Prefix

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

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.

Group Anagrams

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

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...

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...

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 Sudoku

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

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...

Climbing Stairs

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

Longest Palindromic Substring

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

Palindrome Number

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

Rotate Image

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

Spiral Matrix

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

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...

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.

Roman to Integer

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

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...

Search in Rotated Sorted Array

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

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.

Maximum Subarray

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

Merge Two Sorted Lists

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

Generate Parentheses

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

Merge k Sorted Lists

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

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]).

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.

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...

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.

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...

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.

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...

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.

Maximum Depth of Binary Tree

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

Permutations

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

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...

Add Binary

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

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).

Next Permutation

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

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...

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...

Symmetric Tree

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

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:

Validate Binary Search Tree

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

First Missing Positive

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

String to Integer (atoi)

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

Interleaving String

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

Jump Game II

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

Pow(x, n)

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

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...

Wildcard Matching

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

Binary Tree Inorder Traversal

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

Search a 2D Matrix

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

Divide Two Integers

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

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,...

Word Search

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

Balanced Binary Tree

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

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.

Count and Say

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

Subsets

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

Remove Duplicates from Sorted List

Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

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...

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...

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...

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...

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.

Rotate List

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

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.

Integer to Roman

Seven different symbols represent Roman numerals with the following values:

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...

Decode Ways

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

Partition List

Given the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

Combinations

Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

Convert Sorted Array to Binary Search Tree

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

Sudoku Solver

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

Same Tree

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

Length of Last Word

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

Remove Duplicates from Sorted List II

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked li...

Restore IP Addresses

A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.

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...

Edit Distance

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

Permutations II

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

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.

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.

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...

Valid Number

Given a string s, return whether s is a valid number.

Substring with Concatenation of All Words

You are given a string s and an array of strings words. All the strings of words are of the same length.

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...

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...

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...

Flatten Binary Tree to Linked List

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

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.

Subsets II

Given an integer array nums that may contain duplicates, return all possible subsets (the power set).

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...

Search in Rotated Sorted Array II

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