48. 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?

##Approach 1 顺时针每四个元素交换。注意row为0...n/2，column为0...(n+1)/2。

public class Solution {
    public void rotate(int[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return;
        }
        int n = matrix.length;
        for(int i = 0; i < n / 2; i++) {
            for(int j = 0; j < (n + 1) / 2; j++) {
                int temp = 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] = temp;
            }
        }
    }
}

##Approach 2 解题思路为：first reverse up to down, then swap the symmetry

public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return;
        int n =  matrix.length;
        for(int i = 0; i < n / 2; i++) {
            for(int j = 0; j < n; j++) {
                swap(matrix, i, j, n-1-i, j);
            }
        }
        for(int i = 0; i < n; i++) {
            for(int j = i+1; j < n; j++) {
                swap(matrix, i, j, j, i);
            }
        }
        
    }
    
    private void swap(int[][] matrix, int row1, int col1, int row2, int col2) {
        int temp = matrix[row1][col1];
        matrix[row1][col1] = matrix[row2][col2];
        matrix[row2][col2] = temp;
    }
}