LeetCode 48. Rotate Image

Question

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.

https://leetcode.com/problems/rotate-image/

• Solution1

class Solution {
    public void rotate(int[][] matrix) {
        if (matrix == null) return;
        if (matrix.length == 0 || matrix[0].length == 0) return;
        int top = 0;
        int left = 0;
        int right = matrix.length - 1;
        int bottom = matrix.length - 1;
        int n = matrix.length;
        while (n > 1) {
            for (int i = 0; i < n - 1; i++) {
                int tmp = matrix[top][left + i];
                matrix[top][left + i] = matrix[bottom - i][left];
                matrix[bottom - i][left] = matrix[bottom][right - i];
                matrix[bottom][right - i] = matrix[top + i][right];
                matrix[top + i][right] = tmp;
            }
            top++;
            bottom--;
            left++;
            right--;
            n -= 2;
        }
    }
}

Complexity:

Time complexity: O(n^2)

Space complexity: O(1)