[LeetCode]661. Image Smoother 解题报告(C++)

[LeetCode]661. Image Smoother 解题报告(C++)

题目描述

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].

题目大意

• 做一个图片的 3x3 滤波器.
• 注意边界情况的处理.

解题思路

方法1:

• 开一个二维的数据来填值.
• 遍历图像, 给(i,j)为中心的3x3的数组求和做平均.
• 这里要注意边界判断. 统计用了多少个有用的像素.然后做平均

代码实现:

class Solution {
public:
    vector<vector<int>> imageSmoother(vector<vector<int>>& M) {
        int row = M.size();
        int col = M[0].size();

        vector<vector<int>> result;
        result.resize(row);
        for (int i = 0; i < row; i++) {
            result[i].resize(col);
        }

        // 优秀啊!这样做方向移动!!!简直优秀!!!
        vector<vector<int>> dirs = { {-1,-1},{-1,0},{-1,1},
                                    {0,-1},{0,1},
                                    {1,-1},{1,0},{1,1} };

        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                int sum = M[i][j];
                int cnt = 1;
                for (auto dir : dirs) {
                    int x = i + dir[0], y = j + dir[1];
                    if (x < 0 || x >= row || y < 0 || y >= col) {
                        continue;
                    }
                    ++cnt;
                    sum += M[x][y];
                }
                result[i][j] = sum / cnt;
            }

        }
        return result;
    }
};

---

小结

• 方向移动:

  vector<vector<int>> dirs = { {-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1} };

• 边界判断:

  if (x < 0 || x >= row || y < 0 || y >= col) {continue;}