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] ]
先上下翻转，然后在对称翻转。
/*
* 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
*/1 class Solution { 2 3 public void rotate(int[][] matrix) { 4 int rows = matrix.length - 1; 5 int cols = matrix[0].length - 1; 6 for(int i = 0;i <=rows/2;i++) 7 for(int j = 0;j <= cols;j++ ) 8 swap2(matrix,i,j,cols-i,j); 9 10 for(int i = 0;i<=rows;i++) 11 for(int j =i+1;j<=cols;j++) 12 swap2(matrix, i, j,j,i); 13 } 14 15 private void swap2(int[][] a,int i1,int j1,int i2,int j2) { 16 int temp = a[i1][j1]; 17 a[i1][j1] = a[i2][j2]; 18 a[i2][j2] = temp; 19 20 } 21 22 23 24 }