Interview questions

Path Sum II

Find all root-to-leaf paths in a binary tree whose node values sum to targetSum, returning each path as a list of values. This is solved…

Companies: Amazon, Meta, Microsoft, Salesforce

Backtracking · Binary Tree · Depth-First Search · Tree

Last reported May 2026

Network Delay Time

Given a directed, nonnegative-weighted graph and a start node k, compute single-source shortest-path distances and return the maximum distance (the time for the signal to…

Companies: CrowdStrike, NVIDIA

Breadth-First Search · Depth-First Search · Dijkstra's Algorithm · Graph Theory

Last reported Apr 2026

Smallest Common Region

Given lists where each entry names a parent region followed by its immediate subregions and two region names, find their smallest common region — the…

Companies: Airbnb

Array · Binary Lifting · Breadth-First Search · Depth-First Search

Last reported Apr 2026

Making A Large Island

Given an n×n binary grid where you can flip at most one 0 to 1, compute the largest possible 4-directional island size after the flip…

Companies: DoorDash, Meta, TikTok, Uber

Array · Breadth-First Search · Depth-First Search · Matrix

Last reported Mar 2026

Serialize and Deserialize N-ary Tree

Design algorithms to serialize an N-ary tree into a single string and deserialize it back, preserving node values and the arbitrary number and order of…

Companies: Apple, Bloomberg, Rubrik, TikTok

Breadth-First Search · Depth-First Search · String · Tree

Last reported Mar 2026

All Nodes Distance K in Binary Tree

Given a binary tree and a target node value, return all node values at distance K from the target. The challenge is to traverse both…

Companies: Amazon, Meta, Microsoft, TikTok

Binary Tree · Breadth-First Search · Depth-First Search · Hash Table

Last reported Mar 2026

Boundary of Binary Tree

Return the boundary of a binary tree: list nodes on the left boundary top-down (excluding leaves), then all leaves left-to-right, then the right boundary bottom-up…

Companies: Amazon, Meta, Snowflake

Binary Tree · Depth-First Search · Tree

Last reported Feb 2026

Count Pairs of Connectable Servers in a Weighted Tree Network

For each node c in a weighted tree, count unordered pairs of distinct servers (a,b) (neither equal to c) such that the distances from c…

Companies: NVIDIA, Rippling

Array · Depth-First Search · Tree

Last reported Dec 2025

Possible Bipartition

Given n people and pairwise dislikes, determine whether the corresponding undirected graph is bipartite — i.e., whether you can 2-color all vertices (split into two…

Companies: LinkedIn, TikTok, Uber

Bipartite Graph · Breadth-First Search · Depth-First Search · Graph Coloring

Last reported Dec 2025

Amount of Time for Binary Tree to Be Infected

Given a binary tree and a start node, compute how many minutes it takes for an infection that spreads each minute to adjacent nodes (parent/children)…

Companies: Microsoft, Salesforce

Binary Tree · Breadth-First Search · Depth-First Search · Hash Table

Last reported Dec 2025

Count Nodes Equal to Average of Subtree

Count the nodes in a binary tree whose value equals the integer average (floor of sum/count) of all values in their subtree — solved by…

Companies: Meta, Snowflake

Binary Tree · Depth-First Search · Tree

Last reported Aug 2025

Binary Tree Inorder Traversal

Return the node values of a binary tree in inorder (left → root → right) sequence. The recursive solution is trivial; the follow-up asks for…

Companies: Anduril, Meta, Oracle

Binary Tree · Depth-First Search · Stack · Tree

Last reported Jul 2025

Kth Smallest Element in a BST

Return the k-th smallest value (1-indexed) in a BST — exploit that an in-order traversal yields values in sorted order and pick the k-th visited…

Companies: Amazon, Google, Meta, Uber

Binary Search Tree · Binary Tree · Depth-First Search · Tree

Last reported Mar 2025

Contain Virus

Simulate days on an m×n grid where infected cells spread 4-directionally: each day identify all connected infected regions, compute for each the set of uninfected…

Companies: Flipkart, Uber

Array · Breadth-First Search · Depth-First Search · Matrix

Last reported Jan 2025

Smallest String With Swaps

Given a string and allowed index swap pairs, view pairs as edges in a graph to find connected components where characters can be freely permuted…

Companies: Goldman Sachs, Google

Array · Breadth-First Search · Depth-First Search · Hash Table

Last reported Oct 2024

Balanced Binary Tree

Check whether a binary tree is height-balanced, i.e., for every node the heights of its left and right subtrees differ by at most one. With…

Companies: Anduril

Binary Tree · Depth-First Search · Tree

Binary Search Tree to Greater Sum Tree

Transform a BST so each node's value becomes its original value plus the sum of all keys greater than it; this is typically done with…

Companies: Apple

Binary Search Tree · Binary Tree · Depth-First Search · Tree

Binary Tree Preorder Traversal

Return the preorder (root–left–right) traversal of a binary tree as a list of node values. The recursive solution is trivial; the follow-up asks for an…

Companies: Meta

Binary Tree · Depth-First Search · Stack · Tree

Count Paths That Can Form a Palindrome in a Tree

Count pairs of nodes in a rooted tree whose path edge-letters can be rearranged into a palindrome — equivalently, the multiset of letters on the…

Companies: Goldman Sachs

Bit Manipulation · Depth-First Search · Hash Table · Tree

Distance to a Cycle in Undirected Graph

Given an undirected graph, return for every vertex the shortest distance to the nearest vertex that lies on any cycle. Key idea: identify cycle vertices…

Companies: Salesforce

Breadth-First Search · Depth-First Search · Graph Theory · Topological Sort

Loud and Rich

Given an acyclic directed graph of richer->poorer relations and a quietness score per person, compute for each person the quietest person among all people who…

Companies: Flipkart

Array · Depth-First Search · Directed Acyclic Graph · Graph Theory

Maximize Sum of Weights after Edge Removals

Given a weighted tree, remove edges so that each node's degree in the remaining forest is at most k while maximizing the total weight of…

Companies: LinkedIn, Uber

Depth-First Search · Dynamic Programming · Sorting · Tree