题目连接：Leetcode 048 Rotate Image
解题思路：将矩阵分为4块，每次交换4个数。
1 1 1 1 2
4 1 1 1 2
4 4 * 2 2
4 3 3 3 2
4 3 3 3 3
class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
int n = matrix.size();
for (int i = 0; i < n; i++) {
for (int j = i; j < n-i-1; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[n-j-1][i];
matrix[n-j-1][i] = matrix[n-i-1][n-j-1];
matrix[n-i-1][n-j-1] = matrix[j][n-i-1];
matrix[j][n-i-1] = tmp;
}
}
}
};
