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Grokking the Coding Interview Patterns

Solution: Flood Fill

Explore the flood fill algorithm by applying depth-first search to a 2D grid to change connected pixels of the same color. Understand how to use recursion and boundary conditions to effectively perform backtracking and update only valid neighboring cells. This lesson helps you implement an efficient flood fill solution with its time and space complexities explained.

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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. ...