Flood Fill

easycodingAlgorithmsBFSDFSMatrix~20 min

Asked at Google, Meta

Overview

Given an m × n image grid, a starting pixel (sr, sc), and a new color, perform a flood fill: change the starting pixel and all connected pixels with the same original color to the new color. Connected means sharing an edge (up, down, left, right).

Constraints

1 <= m, n <= 50
0 <= image[i][j], color <= 65535
0 <= sr < m, 0 <= sc < n

Examples

floodFill([[1,1,1],[1,1,0],[1,0,1]], 1, 1, 2);
// => [[2,2,2],[2,2,0],[2,0,1]]

Solution

Reveal solution

function floodFill(image, sr, sc, color) {
  const orig = image[sr][sc];
  if (orig === color) return image;
  const m = image.length, n = image[0].length;

  function dfs(r, c) {
    if (r < 0 || r >= m || c < 0 || c >= n) return;
    if (image[r][c] !== orig) return;
    image[r][c] = color;
    dfs(r+1,c); dfs(r-1,c); dfs(r,c+1); dfs(r,c-1);
  }

  dfs(sr, sc);
  return image;
}

Resources

flood-fill.js

Flood Fill

easycodingAlgorithmsBFS

Overview

Given an m × n image grid, a starting pixel (sr, sc), and a new color, perform a flood fill: change the starting pixel and all connected pixels with the same original color to the new color. Connected means sharing an edge (up, down, left, right).

Constraints

1 <= m, n <= 50
0 <= image[i][j], color <= 65535
0 <= sr < m, 0 <= sc < n

Examples

floodFill([[1,1,1],[1,1,0],[1,0,1]], 1, 1, 2);
// => [[2,2,2],[2,2,0],[2,0,1]]

Solution

Reveal solution

function floodFill(image, sr, sc, color) {
  const orig = image[sr][sc];
  if (orig === color) return image;
  const m = image.length, n = image[0].length;

  function dfs(r, c) {
    if (r < 0 || r >= m || c < 0 || c >= n) return;
    if (image[r][c] !== orig) return;
    image[r][c] = color;
    dfs(r+1,c); dfs(r-1,c); dfs(r,c+1); dfs(r,c-1);
  }

  dfs(sr, sc);
  return image;
}

Resources

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