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. You should perform a flood fill on the image starting from the pixel image[sr][sc].

To perform a flood fill, consider the starting pixel, plus any pixels connected 4-directionally to the starting pixel of the same color as the starting pixel, plus any pixels connected 4-directionally to those pixels (also with the same color), and so on. Replace the color of all of the aforementioned pixels with color.

Return the modified image after performing the flood fill.

Constraints

• m == image.length
• n == image[i].length
• 1 <= m, n <= 50
• 0 <= image[i][j], color < 216
• 0 <= sr < m
• 0 <= sc < n

Solution

The problem Flood Fill can be solved using a depth-first search to find grids with the same color as image[sr][sc]. One thing to note is that when image[sr][sc] == color, then the search should not be performed since it can possibly form a infinite loop.

Implementation

static const int fast_io = []()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    return 0;
}();

class Solution
{
  private:
    int old_color;
    int new_color;

  public:
    void helper(vector<vector<int>> &image, int col, int row)
    {
        if (!(0 <= col && col < image.size() && 0 <= row && row < image[0].size()))
            return;
        if (image[col][row] != old_color)
            return;

        image[col][row] = new_color;
        helper(image, col - 1, row);
        helper(image, col, row - 1);
        helper(image, col, row + 1);
        helper(image, col + 1, row);
    }

    vector<vector<int>> floodFill(vector<vector<int>> &image, int sr, int sc, int color)
    {
        old_color = image[sr][sc];
        new_color = color;

        if (old_color != new_color)
            helper(image, sr, sc);
        return image;
    }
};