733. Flood Fill

733. Flood Fill

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.

Example 1:

Input: image = [[1,1,1],[1,1,0],[1,0,1]], sr = 1, sc = 1, color = 2
Output: [[2,2,2],[2,2,0],[2,0,1]]
Explanation: From the center of the image with position (sr, sc) = (1, 1) (i.e., the red pixel), all pixels connected by a path of the same color as the starting pixel (i.e., the blue pixels) are colored with the new color.
Note the bottom corner is not colored 2, because it is not 4-directionally connected to the starting pixel.

My Solutions:

这道题的意思是image[sr][sc]出发，检查所有相邻的格子(当前点以及这个点连接的四个点)，如果格子的颜色和初始格子颜色相同，改变相邻的格子的颜色变成new color。

用dfs的思想，依次检查每个cell的上下左右。

class Solution {
    public int[][] floodFill(int[][] image, int sr, int sc, int color) {
        int oldColor = image[sr][sc];
        if (oldColor != color) dfs(image, sr, sc, oldColor, color);
        return image;
    }
    
    private void dfs(int[][] image, int r, int c, int color, int newColor) {
        if (r < 0 || r >= image.length || c < 0 || c >= image[0].length) return;
        if (image[r][c] == color) {
            image[r][c] = newColor;
            dfs(image, r + 1, c, color, newColor);
            dfs(image, r - 1, c, color, newColor);
            dfs(image, r, c + 1, color, newColor);
            dfs(image, r, c - 1, color, newColor);
        }
    }
}