733. Flood Fill

Posted 2020-10-16 Zzz...y

An image is represented by a 2-D array of integers, each integer representing the pixel value of the image (from 0 to 65535).

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.

At the end, return the modified image.

Example 1:

Input: 
image = [[1,1,1],[1,1,0],[1,0,1]]
sr = 1, sc = 1, newColor = 2
Output: [[2,2,2],[2,2,0],[2,0,1]]
Explanation: 
From the center of the image (with position (sr, sc) = (1, 1)), all pixels connected 
by a path of the same color as the starting pixel 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.

给一个起始点，替换新值。并把与该点四联通区域内的值相同的点一并替换。对“四联通点”的符合条件的四联通点也同样操作。

这个跟图像处理里面的“种子点生长”很像，给定一个种子点，不断扩张，直至把所有联通的区域填满。

遍历所有符合的点就可以了，深度优先或广度优先都可以用。

深度优先的代码：

class Solution {
public:
    vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int newColor) {
        int row = image.size();
        int col = image[0].size();
        int rec = image[sr][sc];
        if (rec==newColor) return image;
        image[sr][sc] = newColor;
        if(sr-1>=0 && image[sr-1][sc]==rec)  floodFill(image, sr-1, sc, newColor);
        if(sr+1<row && image[sr+1][sc]==rec)  floodFill(image, sr+1, sc, newColor);
        if(sc-1>=0 && image[sr][sc-1]==rec)  floodFill(image, sr, sc-1, newColor);
        if(sc+1<col && image[sr][sc+1]==rec)  floodFill(image, sr, sc+1, newColor);
        return image;
    }
};