Flood fill Algorithm

An image is represented by a 2-D array of integers, each integer representing the pixel value of the image.

Given a coordinate (sr, sc) representing the starting pixel (row and column) of the flood fill, and a pixel value newColor, “flood fill” the image.

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 as the starting pixel), and so on. Replace the color of all of the aforementioned pixels with the newColor.

• Time : O(nm)
• Space : O(nm)

class Solution {
    void ff(vector<vector<int>>& image, int y, int x, int from, int& to) {
        if(0 <= y and y < image.size() and 0 <= x and x < image[0].size() and image[y][x] == from) {
            image[y][x] = true;
            ff(image, y + 1, x, from, to);
            ff(image, y - 1, x, from, to);
            ff(image, y, x + 1, from, to);
            ff(image, y, x - 1, from, to);
        }
    }
public:
    vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int newColor) {
        if(image[sr][sc] != newColor)
            ff(image, sr, sc, image[sr][sc], newColor);
        return image;
    }
};