Question
You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
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.
Difficulty:Medium
Category:Array
Analyze
Solution
class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
const unsigned int n = matrix.size();
// 1. 沿着对角线翻转一次
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n - i; ++j) {
swap(matrix[i][j], matrix[n - 1 - j][n - 1 - i]);
}
}
// 2. 沿着水平中间线翻转一次
for (int i = 0; i < n / 2; ++i) {
for (int j = 0; j < n; ++j) {
swap(matrix[i][j], matrix[n - 1 - i][j]);
}
}
}
};