leetcode 661 Image Smoother

题目详情

Given a 2D integer matrix M representing the gray scale of an image, you need to design a smoother to make the gray scale of each cell becomes the average gray scale (rounding down) of all the 8 surrounding cells and itself. If a cell has less than 8 surrounding cells, then use as many as you can.

输入一个整数二维数组，输出一个大小相同的二维数组，其中每个元素的值，代表着输入数组M同样位置的元素的周围元素的平均值（包括自己）。

Example 1:
Input:
[[1,1,1],
[1,0,1],
[1,1,1]]
Output:
[[0, 0, 0],
[0, 0, 0],
[0, 0, 0]]
Explanation:
For the point (0,0), (0,2), (2,0), (2,2): floor(3/4) = floor(0.75) = 0
For the point (0,1), (1,0), (1,2), (2,1): floor(5/6) = floor(0.83333333) = 0
For the point (1,1): floor(8/9) = floor(0.88888889) = 0

思路

• 特殊情况就是矩阵的四角的相邻元素只有3个。
• 其余的处于最外围一圈的元素的相邻元素只有5个。

解法

    public int[][] imageSmoother(int[][] M) {
        if(M == null)return null;
        int rows = M.length;
        if(rows == 0)return new int[0][];
        
        int cols = M[0].length;
        
        int[][] res = new int[rows][cols];
        
        for(int row=0;row<rows;row++){
            for(int col =0;col < cols;col++){
                int count = 0;
                int sum = 0;
                for(int incR : new int[]{-1,0,1}){
                    for(int incC : new int[]{-1,0,1}){
                        if(isValid(rows,cols,row+incR,col+incC)){
                            count++;
                            sum += M[row+incR][col+incC];
                        }
                    }
                }
                res[row][col] = sum/count;
            }    
        }

        return res;
    }
    
    public boolean isValid(int row,int col,int x,int y){
        return x >= 0 && x < row && y >= 0 && y < col;
        
    }