LeetCode Q48 Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

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.

public void rotate(int[][] matrix) {
    //以对角线为轴交换
    for (int i = 0; i <  matrix.length; i++) 
    {
        //j <= i 确保交换除了【0，0】，【1，1】和 【2，2】位置的数
        for (int j = 0; j <=i; j++) 
        {
            if (i == j) {
                continue;
            }
            
            int temp = matrix[i][j];
            matrix[i][j] = matrix[j][i];
            matrix[j][i] = temp;
        }
    } 
    //交换column
    //左半边的值是i，右半边的值是j
    //j从最右边开始，与最左边的竖着交换，j往左递减
    for (int i = 0, j = matrix.length - 1; i < matrix.length / 2; i++, j--) 
    {
        for (int k = 0; k < matrix.length; k++) {
            int temp = matrix[k][i];
            matrix[k][i] = matrix[k][j];
            matrix[k][j] = temp;
        }
    }

}