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Grokking the Coding Interview Patterns in JavaScript

Solution: Flood Fill

Explore how to apply backtracking with depth-first search to implement the flood fill algorithm on a 2D grid. This lesson helps you understand how to recursively update connected pixels that share the same original color as the starting pixel. You will learn boundary checks, recursion termination, and how to efficiently fill regions without unnecessary changes.

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Statement

You are given a 2D grid of size m x n, where grid[i][j] represents the pixel value at position (i, j).

Additionally, you are given three integers:

  • sr: The row index of the starting pixel

  • sc: The column index of the starting pixel

  • target: The new color to apply

Your task is to perform a flood fill starting from the pixel at position (sr, sc). Below is the flood fill process:

  1. If the pixel at (sr, sc) already has the value target, return the original grid without any changes.

  2. Otherwise, start at the pixel grid[sr][sc] and change its color to the given color target. ...