Depth-First Search

Explore as far as possible down one path before backtracking, used to walk trees, graphs, and grids.

Depth-First Search Practice Problems

Easy

3 problems

32
Flood Fill
Change the color of a connected region in an image, starting from one pixel.
easy
33
Maximum Depth of Binary Tree
Find the number of nodes along the longest path from the root of a tree to a leaf.
easy
210
Path Sum
Check whether a binary tree has a root-to-leaf path that adds up to a target sum.
easy

Medium

3 problems

34
Pacific Atlantic Water Flow
Find every cell in a grid from which water can flow to both of two opposite oceans.
medium
35
Surrounded Regions
Flip every region of a grid that is fully surrounded by the opposite value.
medium
211
Number of Islands
Count the number of connected land regions in a grid.
medium

Hard

2 problems

Last updated 12 September 2026

Related concepts

Topic	Description
Breadth-First Search	Explore level by level from a starting point, the go-to way to find the shortest path in an unweighted graph.
Graphs	Nodes and edges modeling networks, dependencies, and paths.
Trees	Hierarchical nodes with parent–child links for ordered and nested data.
Backtracking	Try a choice, keep going, and undo it if it fails, used to generate permutations, combinations, and valid layouts.
Topological Sort	Order the nodes of a graph so every task comes after everything it depends on, used for scheduling and build order.
Dijkstra's Algorithm	Find the shortest path from a starting node to every other node in a graph where edges have non-negative weights.