Rotate Image

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

• Time: O(n)
• Space: O(1)

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

private void swap(int[][] matrix, int i1, int j1, int i2, int j2) {
    int temp = matrix[i1][j1];
    matrix[i1][j1] = matrix[i2][j2];
    matrix[i2][j2] = temp;
}