Coding interview problems

Find the indices of two distinct values whose sum matches a target.

Sort and merge every overlapping or touching interval into a disjoint list.

Return a string with every character in reverse order without changing characters.

Find the longest leading substring shared by every string in a list.

Determine whether a phrase reads the same after ignoring case and non-alphanumeric characters.

Count every contiguous substring that reads the same forward and backward.

Return the longest contiguous substring that is a palindrome.

Check whether the values represented by a singly linked list form a palindrome.

Convert a valid canonical Roman numeral into its integer value.

Generate every letter combination represented by digits on a telephone keypad.

Validate that every bracket closes in the correct order and with the matching type.

Return the starting index of the first exact occurrence of one string inside another.

Measure the final whitespace-delimited word in a string.

Generate an n-by-n matrix filled clockwise in spiral order.

Produce the classic FizzBuzz sequence using divisibility rules.

Determine whether any integer appears more than once in an array.

Return the largest sum obtainable from a non-empty contiguous subarray.

Compute the zero-indexed Fibonacci number with an iterative recurrence.

Compute the product of all positive integers up to a non-negative input.

Move every zero to the end while preserving non-zero element order.

Find the only value that is not paired using constant extra space.

Find the best profit from one buy followed by one later sale.

Check whether two lowercase strings contain identical character frequencies.

Locate a target in a sorted unique array using logarithmic search.

Count ASCII vowels in a string without changing other characters.

Count ordered one-step and two-step paths to the top of a staircase.

Build prefix and suffix products without division.

Compute water trapped between elevation bars after rainfall.

Measure the minimum insertions, deletions, and replacements between two strings.

Find the combined median without fully merging two sorted arrays.

Measure the longest contiguous substring of balanced parentheses.

Determine whether a base-10 integer reads identically in reverse.

Add one to a number represented as an array of digits.

Find the element that appears more than half the time in an array.

Check whether one string is a subsequence of another.

Find the index of the first non-repeating character in a string.

Return the index where a target should be inserted into a sorted array.

Maximize the loot from non-adjacent houses along a street.

Decide whether you can reach the last index of an array of jump lengths.

Find the fewest coins needed to make up a given amount.

Find the length of the longest substring without repeating characters.

Find two lines that together with the x-axis hold the most water.

Count the number of islands in a grid of land and water cells.

Determine whether a string can be segmented into words from a dictionary.

Find the length of the longest strictly increasing subsequence.

Find the area of the largest rectangle that fits under a histogram.

Return the maximum of every contiguous window of size k.

Find the minimum number of jumps needed to reach the last index.

Reverse a singly linked list in place using real ListNode structures.

Find the maximum depth of a binary tree using real TreeNode structures.

Determine whether all courses can be completed given prerequisite pairs.

Find how many minutes are needed for rot to spread to every fresh orange.

Find the edge that creates a cycle in an otherwise tree-shaped graph.

Return the kth largest value without requiring a fully sorted array.

Return the k values that occur most often in an integer array.

Generate every subset in the power set of a distinct integer array.

Swap every binary-tree node's left and right children.

Determine whether two binary trees have identical structure and values.

Check whether a binary tree satisfies strict BST ordering.

Return binary-tree values grouped by breadth-first level.

Find the lowest shared ancestor of two values in a binary search tree.

Merge two sorted linked lists by rewiring their nodes.

Detect a cycle from a linked list represented by next-node indices.

Reorder a linked list by alternating nodes from its front and back.

Deep-copy a connected graph from its adjacency-list representation.

Find grid cells that can flow to both oceans under height constraints.

Compute how long a weighted directed network takes to receive a signal.

Merge k sorted sequences using a heap of current candidates.

Return the median after incrementally inserting every stream value.

Generate every ordering of a distinct integer array.

Find target-sum combinations when candidate values may be reused.

Find a word by backtracking through adjacent grid cells.

Execute insert, exact-search, and prefix-search operations on a trie.

Build a trie that supports exact letters and wildcard searches.

Simulate a bounded least-recently-used key-value cache.

Count distinct top-left to bottom-right grid paths moving only right or down.

Build the first numRows rows of Pascal's triangle by summing adjacent values.

Count prime numbers strictly below n with the Sieve of Eratosthenes.

Return the floored integer square root without a built-in sqrt function.

Decide whether summing squared digits eventually reaches one or cycles.

Convert a spreadsheet column title like AB into its 1-based number.

Insert one interval into sorted disjoint intervals and merge any overlaps.

Remove the fewest intervals so the remaining schedule has no overlaps.

Sort an array of 0s, 1s, and 2s in one in-place pass.

Count how many disconnected city groups exist in an undirected connectivity matrix.

Find the shortest contiguous subarray whose sum reaches a target.

Find every unique triplet of numbers in an array that sums to zero.

Rotate an n x n matrix 90 degrees clockwise and return the rotated matrix.

Find a target value's index in an ascending array that has been rotated at an unknown pivot.

Find the length of the longest run of consecutive integers in an unsorted array.

Add two integers together without using the + or - operators.

Check whether a binary tree is a mirror image of itself around its center.

Find the length in edges of the longest path between any two nodes in a binary tree.

Return the k-th smallest value stored in a binary search tree.

Add two non-negative integers represented as reversed-digit linked lists.

Delete the n-th node from the end of a singly linked list in one pass.

Determine whether a binary tree has a root-to-leaf path whose values sum to a target.

Build a height-balanced binary search tree from an ascending array of unique integers.

Reverse only the nodes between two 1-indexed positions of a singly linked list, in one pass.

Swap every adjacent pair of nodes in a singly linked list without changing the node values.

Return the values visible when looking at a binary tree from the right side, ordered top to bottom.

Overlay two binary trees, summing values where both trees have a node.

Find every root-to-leaf path in a binary tree whose values sum to a target.

Rebuild a unique binary tree from its preorder and inorder traversal arrays.

Find the index where a cycle begins in a linked list represented by next-node indices, or -1 if there is none.

Regroup a singly linked list so all odd-positioned nodes come before all even-positioned nodes, preserving relative order within each group.

Find the minimum timeline length needed to schedule tasks with a cooldown between identical letters.

Count how many disconnected components remain in an undirected graph with labeled vertices.

Return every way to cut a string into palindromic substrings, ordered by DFS prefix exploration.

Find all dictionary words that can be traced through adjacent board cells without reusing a cell.

Find the length of the shortest one-letter transformation sequence from a start word to an end word.

Return how many days each temperature must wait until a warmer reading appears.

Count how many valid A1Z26 decodings a digit string can represent.

Find the unique starting station that lets you complete a circular route, or report failure.

Recover a valid alien letter order from a sorted word list, returning the lexicographically smallest valid order.

Find the largest sum obtainable from any non-empty path inside a binary tree.

Return the minimum number of meeting rooms needed so every interval can be scheduled without overlap.

Find the shortest substring of s that still contains every character required by t, including duplicates.

Find the maximum path length you can build by moving to orthogonally adjacent cells with strictly larger values.

Process point updates and inclusive range-sum queries efficiently over the same integer array.

Find the least expensive route from src to dst when you may use at most k intermediate stops.