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.
Example 1:
Given input matrix = [ [1,2,3], [4,5,6], [7,8,9] ], rotate the input matrix in-place such that it becomes: [ [7,4,1], [8,5,2], [9,6,3] ]
Example 2:
Given input matrix = [ [ 5, 1, 9,11], [ 2, 4, 8,10], [13, 3, 6, 7], [15,14,12,16] ], rotate the input matrix in-place such that it becomes: [ [15,13, 2, 5], [14, 3, 4, 1], [12, 6, 8, 9], [16, 7,10,11] ]
/*
* clockwise rotate
* first reverse up to down, then swap the symmetry
* 1 2 3 7 8 9 7 4 1
* 4 5 6 => 4 5 6 => 8 5 2
* 7 8 9 1 2 3 9 6 3
*/
先按行上限翻转, 第1行和最后一行交换, 第i行和第n-i行交换
然后再按对角线交换...惊呆了class Solution { public: void rotate(vector<vector<int>>& matrix) { reverse(matrix.begin(),matrix.end()); for(int i=0;i<matrix.size();++i) for(int j=i+1;j<matrix[0].size();++j) swap(matrix[i][j],matrix[j][i]); } };
原文：https://www.cnblogs.com/lychnis/p/11749147.html