题目:
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] ]
分析:
很明显,题目要求矩阵顺时针旋转90度,且要求不开辟新的空间。我们可以先求矩阵的转置,之后再将转置好的矩阵前后列交换,如下图。
程序:
class Solution { public: void rotate(vectorint>>& matrix) { int n = matrix.size(); for (int i = 0; i < n-1; i++){ for (int j = i+1; j < n; j++){ swap(matrix[i][j], matrix[j][i]); } } for (int i = 0; i < n/2; i++){ for (int j = 0; j < n; j++){ swap(matrix[j][i],matrix[j][n-1-i]); } } } };