Rotate Image 旋转矩阵 @LeetCode

貌似是careercup原题

package Level4;

/**
 * Rotate Image 
 * 
 * You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?
 *
 */
public class S48 {

	public static void main(String[] args) {

	}

	// 矩阵顺时针转90度：先沿中线水平翻转，再沿着对角线翻转
	// eg: 
	/*
	  		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
	 */
	public void rotate(int[][] matrix) {
		int len = matrix.length;
		
		// 先沿中线水平翻转
		for(int i=0; i<len/2; i++){
			for(int j=0; j<len; j++){
				int tmp = matrix[i][j];
				matrix[i][j] = matrix[len-1-i][j];
				matrix[len-1-i][j] = tmp;
			}
		}
		
		// 再沿着对角线翻转
		for(int i=0; i<len; i++){
			for(int j=i+1; j<len; j++){
				int tmp = matrix[i][j];
				matrix[i][j] = matrix[j][i];
				matrix[j][i] = tmp;
			}
		}
	}
}

public class Solution {
    public void rotate(int[][] matrix) {
        int rows = matrix.length;
        int cols = matrix[0].length;
        
        for(int i=0; i<rows/2; i++){
            for(int j=0; j<cols; j++){
                swap(matrix, i, j, rows-1-i, j);
            }
        }
        
        for(int i=0; i<rows; i++){
            for(int j=i; j<cols; j++){
                swap(matrix, i, j, j, i);
            }
        }
    }
    
    public void swap(int[][] matrix, int x1, int y1, int x2, int y2){
        int tmp = matrix[x1][y1];
        matrix[x1][y1] = matrix[x2][y2];
        matrix[x2][y2] = tmp;
    }
}