Oracle Coding Interview Questions

LRU Cache

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

Number of Islands

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

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.

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...

Group Anagrams

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

Longest Palindromic Substring

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

Merge k Sorted Lists

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

Search in Rotated Sorted Array

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

Sliding Window Maximum

You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see...

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]).

Binary Tree Right Side View

Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Longest Consecutive Sequence

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

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...

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.

Reverse Linked List

Given the head of a singly linked list, reverse the list, and return the reversed list.

Merge Two Sorted Lists

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

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.

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] = [ai, b...

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.

Pow(x, n)

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

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...

Gas Station

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

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...

Course Schedule II

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] = [ai, b...

Search a 2D Matrix II

Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties:

Binary Tree Zigzag Level Order Traversal

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

First Missing Positive

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

Word Search

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

Longest Common Prefix

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

Maximum Subarray

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

Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Kth Largest Element in an Array

Given an integer array nums and an integer k, return the kth largest element in the array.

Product of Array Except Self

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

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.

Validate Binary Search Tree

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

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.

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...

Lowest Common Ancestor of a Binary Tree

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

Linked List Cycle

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

Maximal Square

Given an m x n binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.

Valid Anagram

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

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...

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.

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.

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...

Generate Parentheses

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

Delete Node in a Linked List

There is a singly-linked list head and we want to delete a node node in it.

Jump Game II

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

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.

Rotate Image

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

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...

Isomorphic Strings

Given two strings s and t, determine if they are isomorphic.

Majority Element

Given an array nums of size n, return the majority element.

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...

Integer to Roman

Seven different symbols represent Roman numerals with the following values:

Minimum Size Subarray Sum

Given an array of positive integers nums and a positive integer target, return the minimal length of a subarray whose sum is greater than or equal to target. If...

Kth Smallest Element in a BST

Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree.

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.

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...

Longest Valid Parentheses

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

Rotate Array

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.

Permutations

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

Largest Number

Given a list of non-negative integers nums, arrange them such that they form the largest number and return it.

Decode Ways

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

Sudoku Solver

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

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...

Rotate List

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

Regular Expression Matching

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

Find Peak Element

A peak element is an element that is strictly greater than its neighbors.

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...

Invert Binary Tree

Given the root of a binary tree, invert the tree, and return its root.

Palindrome Number

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

Max Points on a Line

Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane, return the maximum number of points that lie on the same straight line.

Populating Next Right Pointers in Each Node

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:

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...

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.

Two Sum II - Input Array Is Sorted

Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number....

Palindrome Linked List

Given the head of a singly linked list, return true if it is a palindrome or false otherwise.

Sort List

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

Basic Calculator

Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.

Find Subsequence of Length K With the Largest Sum

You are given an integer array nums and an integer k. You want to find a subsequence of nums of length k that has the largest sum.

Path Sum II

Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path...

Implement Queue using Stacks

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, an...

Count Number of Pairs With Absolute Difference K

Given an integer array nums and an integer k, return the number of pairs (i, j) where i < j such that |nums[i] - nums[j]| == k.

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...

Excel Sheet Column Title

Given an integer columnNumber, return its corresponding column title as it appears in an Excel sheet.

Number of Unique Good Subsequences

You are given a binary string binary. A subsequence of binary is considered good if it is not empty and has no leading zeros (with the exception of "0").

Implement Stack using Queues

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and...

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...

Intersection of Two Linked Lists

Given the heads of two singly linked-lists headA and headB, return the node at which the two lists intersect. If the two linked lists have no intersection at al...

Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

Climbing Stairs

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

Pascal's Triangle

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

Delete Duplicate Emails

Table: Person

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:

Maximum Product Subarray

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

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.