Leetcode48 Rotate Image

Rotate Image

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Solution1

• 这道题无非是一些边界条件的把握。

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

Solution2

• 有更加trick的解法，如下

public class Solution {
    public void rotate(int[][] matrix) {
        for(int i=0,j=matrix.length-1;i<j;i++,j--){
            int[] temp = matrix[i];
            matrix[i] = matrix[j];
            matrix[j] = temp;
        }
        for(int i=0;i<matrix.length;i++){
            for(int j=0;j<i;j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }
}

更详细的解释在顺时针和逆时针都可以用类似方法