Flood Fill

Problem

An image is represented by an m x n integer grid image where image[i][j] represents the pixel value of the image. You are also given three integers sr, sc, and color. Perform a flood fill starting from the pixel image[sr][sc].

Examples

The brute-force approach

For each candidate cell, trace every possible path from the start position and check if the cell is reachable through same-color neighbors.

# No meaningful brute force: connectivity can only be determined
# by actually exploring outward from the starting pixel.
# The DFS approach IS the direct solution, there's no simpler version.

Checking connectivity naively for each cell would mean re-scanning the grid repeatedly. O((m×n)²). The only efficient way to find the connected region is to explore outward from the start in one pass.

Spotting the pattern

This is a Graph Traversal problem. The key question to ask yourself:

How do I visit every cell in the connected region exactly once, without revisiting?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.