Flood Fill：搜索二维数组中相邻的相同元素并替换

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.

Note:

The length of 

image

 and 

image[0]

 will
be in the range 

[1, 50]

.
The given starting pixel will satisfy 

0 <= sr < image.length

 and 

0
<= sc < image[0].length

.
The value of each color in 

image[i][j]

 and 

newColor

 will
be an integer in 

[0, 65535]

.
解释：就是类似于画图里颜色填充的那种，把二维数组中相邻且相同的元素替换成其他元素。

思路：递归遍历替换即可，注意边界，以及本身已经符合要求的颜色就无需替换的这种情况。

class Solution {
public void recursion(int[][] image, int precolor ,int targetcolor , int x,int y){
if(x < 0|| x >= image.length ) return ;
if(y < 0|| y >= image[0].length ) return ;
if(image[x][y]!=precolor) return ;
if(image[x][y]==targetcolor) return ;//原本就是同色，无序变动；这点要注意，易错
image[x][y] = targetcolor;
recursion(image,precolor ,targetcolor ,x+1,y);
recursion(image,precolor ,targetcolor ,x-1,y);
recursion(image,precolor ,targetcolor ,x,y+1);
recursion(image,precolor ,targetcolor ,x,y-1);
}

public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {

if(sr < 0|| sr >= image.length ) return image;
if(sc < 0|| sc>= image[0].length ) return image;
int precolor = image[sr][sc];
recursion(image,precolor,newColor,sr,sc);
return image;
}
}