Coding Interview Questions

Given daily prices of a stock, find the maximum profit from a single buy followed by a later sell. If no profitable transaction exists, the profit is zero.

Given a list of integers sorted ascending and a target, return the index of the target if present, otherwise negative one. The search must run in logarithmic time.

You are climbing a staircase that takes n steps to reach the top. Each move you may climb one or two steps. Count the number of distinct ways to reach the top.

Given a list of integers, decide whether any value appears more than once. Return true if at least one value is repeated, otherwise false.

Given a number n, return the sequence from one to n where multiples of three become Fizz, multiples of five become Buzz, multiples of both become FizzBuzz, and all other numbers stay as their string form.

Given the root of a binary tree, produce its mirror image by swapping the left and right child of every node. Return the root of the inverted tree.

Given the head of a singly linked list, decide whether it contains a cycle, meaning some node's next pointer eventually revisits an earlier node. Use constant extra space.

Given the root of a binary tree, return its maximum depth, defined as the number of nodes along the longest path from the root down to a leaf.

Given the heads of two singly linked lists already sorted ascending, splice them into one sorted list and return its head. Reuse the existing nodes.

Given the head of a singly linked list, reverse the list in place and return the new head. The reversal should rewire the existing nodes rather than copying values.

Given a Roman numeral string, convert it to its integer value. A smaller numeral placed before a larger one is subtracted rather than added.

Given the roots of two binary trees, decide whether they are structurally identical and hold the same values at every position. Return true only if both shape and values match.

Given a list of integers and a target value, find the two distinct positions whose values add up to the target. Return those two positions. Assume exactly one such pair exists.

Given two strings, determine whether one is a rearrangement of the other. Two strings are anagrams when they contain exactly the same characters with the same frequencies.

Given a string, decide whether it reads the same forwards and backwards once you ignore case and consider only alphanumeric characters. Return true if it is such a palindrome.

Given a string of bracket characters drawn from round, square, and curly pairs, decide whether every opening bracket is closed by the correct type in the correct order. Return true if the string is well balanced.

Given a list of integers, find every unique triple of values that sums to zero. Return the list of triples without duplicates.

Given the root of a binary tree, return its node values grouped level by level from top to bottom, each level read left to right.

Given a reference to a node in a connected undirected graph, return a deep copy of the whole graph. Each cloned node must hold the same value and a list of its cloned neighbours.

Given coin denominations and a target amount, return the fewest coins needed to make exactly that amount. If it cannot be made, return negative one. You have an unlimited supply of each coin.

Given distinct positive candidates and a target, return all unique combinations that sum to the target. Each candidate may be used any number of times, and combinations differing only in order count once.

Given a list of non-negative heights, each representing a vertical line on a number line, find two lines that together with the x-axis hold the most water. Return that maximum area.

Given a number of courses and a list of prerequisite pairs, decide whether you can finish all courses. You can finish them only if the prerequisite relationships contain no cycle.

Given a list of daily temperatures, for each day return how many days you must wait until a warmer temperature. If no warmer day exists, the answer for that day is zero.

Design an encoder that serializes a list of arbitrary strings into one string, and a decoder that recovers the original list. The strings may contain any characters, including your delimiters.

Given a list of tokens representing an arithmetic expression in postfix (Reverse Polish) notation, evaluate it. Operators are the four basic arithmetic operations and operands are integers.

Given an ascending array of unique values rotated at an unknown pivot, return the minimum element in logarithmic time.

Given a list of strings, cluster them so that words which are anagrams of each other land in the same group. Return the list of groups in any order.

Given the amounts of money in a row of houses, find the maximum you can rob without taking from two adjacent houses, since adjacent robberies trigger the alarm.

Design a prefix tree supporting inserting a word, checking whether a full word exists, and checking whether any stored word starts with a given prefix.

Given a list of non-overlapping intervals sorted by start and a new interval, insert it and merge any overlaps so the result stays sorted and non-overlapping.

Given a list where each value is the maximum forward jump from that position, decide whether you can reach the last index starting from the first.

Given piles of bananas and a number of hours, find the smallest integer eating speed such that all piles are finished within the time. Each hour Koko eats from one pile up to her speed, finishing partial piles in that hour.

Given a list of integers and a number k, return the kth largest element in sorted order, where duplicates count as distinct positions. Aim for better than a full sort.

Given an unsorted list of integers, find the length of the longest run of consecutive values. The values do not need to be adjacent in the list. Aim for linear time.

Given a list of integers, return the length of the longest strictly increasing subsequence. The chosen elements need not be contiguous but must keep their original order.

Given a string of uppercase letters and a budget k, find the length of the longest substring you can make all-identical by replacing at most k characters.

Given a string, find the length of the longest contiguous substring that contains no repeated character.

Given the root of a binary search tree and two of its nodes, return their lowest common ancestor, the deepest node that has both given nodes as descendants. A node may be a descendant of itself.

Design a cache with a fixed capacity that supports get and put in constant time. When the cache is full and a new key is added, evict the least recently used entry. Reading or updating a key marks it most recently used.

Given a list of integers, find the contiguous subarray with the largest sum and return that sum. The subarray must contain at least one element.

Given a list of intervals, merge every set of overlapping intervals and return the resulting non-overlapping intervals covering the same ranges.

Design a stack that supports push, pop, top, and retrieving the current minimum, with every operation running in constant time. The minimum must reflect only the values currently on the stack.

Given a list of intervals, return the minimum number you must remove so that the remaining intervals do not overlap.

Given a grid of land and water cells, count the number of islands. An island is a group of land cells connected horizontally or vertically, and is surrounded by water or the grid edge.

Given a list of positive integers, decide whether it can be split into two groups whose sums are equal.

Given two strings, decide whether the second contains any contiguous substring that is a permutation of the first. Return true if such a window exists.

Given a list of distinct integers, return every possible ordering of them. The list of permutations may be returned in any order.

Given a list of integers, return a new list where each position holds the product of every other value in the original list. Solve it without using division.

Given the head of a singly linked list and a number n, remove the nth node counting from the end and return the head. Do it in a single pass.

Given a singly linked list, reorder it so it interleaves the first node, the last node, the second node, the second-to-last node, and so on. Rewire nodes in place without changing their values.

Given an n by n matrix representing an image, rotate it ninety degrees clockwise in place without allocating another matrix.

Given an ascending array that has been rotated at an unknown pivot, find the index of a target value or return negative one. Achieve logarithmic time.

Given a list of integers and a target k, count how many contiguous subarrays sum to exactly k. Values may be negative.

Given a list of distinct integers, return all possible subsets, including the empty set and the full set. The collection of subsets is the power set and may be returned in any order.

Given a list of integers and a number k, return the k values that occur most frequently. The answer may be returned in any order, and the k most frequent values are guaranteed to be unambiguous.

Given a list of integers already sorted in non-decreasing order and a target, return the one-based positions of the two values that add up to the target. Use constant extra space.

A robot starts at the top-left of an m by n grid and may move only right or down. Count the number of distinct paths it can take to reach the bottom-right corner.

Given a partially filled 9x9 grid, decide whether the current placement is valid. Each row, each column, and each of the nine 3x3 sub-boxes must contain no repeated digit. Empty cells are ignored.

Given the root of a binary tree, decide whether it is a valid binary search tree, meaning every node's value is greater than all values in its left subtree and smaller than all in its right subtree.

Given a string and a dictionary of words, decide whether the string can be segmented into a sequence of one or more dictionary words. Words may be reused.

Given a grid of letters and a word, decide whether the word can be spelled by a path of adjacent cells moving horizontally or vertically. The same cell may not be reused within one path.

Given two strings, return the minimum number of single-character insertions, deletions, or substitutions needed to transform the first into the second.

Design a structure that accepts a stream of integers and can report the running median at any time. Support adding a number and querying the current median efficiently.

Given two ascending sorted arrays, return the median of their combined ordering in logarithmic time relative to the smaller array.

Given an array of k singly linked lists, each sorted ascending, merge them all into one sorted linked list and return its head.

Given a string s and a pattern t, find the shortest contiguous substring of s that contains every character of t including duplicates. If none exists, return an empty string.

Given a number n, place n queens on an n by n chessboard so that no two attack each other, and return all distinct board configurations. Queens attack along rows, columns, and both diagonals.

Given a list of non-negative bar heights forming an elevation map, compute how many units of water are trapped after rain. Water sits in the dips between taller bars.

Given a start word, an end word, and a dictionary of equal-length words, find the length of the shortest transformation sequence that changes the start into the end, altering exactly one letter at a time and keeping every intermediate word in the dictionary. Return zero if impossible.