LeetCode Image Smoother

Posted 2020-10-07 Dylan_Java_NYC

原题链接在这里：https://leetcode.com/problems/image-smoother/description/

题目：

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.

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

Note:

1. The value in the given matrix is in the range of [0, 255].
2. The length and width of the given matrix are in the range of [1, 150].

题解：

看周围8个点加自己是否是boundary内，若在就更新sum, count++. 最后计算floor average.

Time Complexity: O(m*n), m = M.length, n = M[0].length.

Space: O(m*n), res size.

AC Java:

 1 class Solution {
 2     public int[][] imageSmoother(int[][] M) {
 3         if(M == null || M.length == 0 || M[0].length == 0){
 4             return M;
 5         }
 6         
 7         int m = M.length;
 8         int n = M[0].length;
 9         int [][] res = new int[m][n];
10         
11         for(int i = 0; i<m; i++){
12             for(int j = 0; j<n; j++){
13                 int count = 0;
14                 int sum = 0;
15                 for(int iInc : new int[]{-1,0,1}){
16                     for(int jInc : new int[]{-1,0,1}){
17                         if(isValid(i+iInc, j+jInc, m, n)){
18                             count++;
19                             sum += M[i+iInc][j+jInc];
20                         }
21                     }
22                 }
23                 res[i][j] = sum/count;
24             }
25         }
26         return res;
27     }
28     
29     private boolean isValid(int i, int j, int m, int n){
30         return i>=0 && i<m && j>=0 && j<n;
31     }
32 }