48-翻转图像

LeetCode 48. Rotate Image

LeetCode-48

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]

method

i表示要处理的行数，j表示要处理的列数，i可以就n/2，但j要(n+1)/2，囊括要处理的区域

难点：下标的推导

void rotate(vector<vector<int>>& matrix) {
    int n = matrix.size();
    for (int i = 0; i < n / 2; i++) {
        for (int j = 0; j < (n + 1) / 2; j++) {
            int tmp = matrix[i][j];
            matrix[i][j] = matrix[n-1-j][i];
            matrix[n-1-j][i] = matrix[n-1-i][n-1-j];
            matrix[n-1-i][n-1-j] = matrix[j][n-1-i];
            matrix[j][n-1-i] = tmp;
        }
    }
}