LeetCode-in-All

48. Rotate Image

Medium

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.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]

Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:

Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]

Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]

Constraints:

• n == matrix.length == matrix[i].length
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

Solution

class Solution {
  void rotate(List<List<int>> matrix) {
    int n = matrix.length;

    for (int i = 0; i < n ~/ 2; i++) {
      for (int j = i; j < n - i - 1; j++) {
        List<List<int>> pos = [
          [i, j],
          [j, n - 1 - i],
          [n - 1 - i, n - 1 - j],
          [n - 1 - j, i]
        ];

        int t = matrix[pos[0][0]][pos[0][1]];
        for (int k = 1; k < pos.length; k++) {
          int temp = matrix[pos[k][0]][pos[k][1]];
          matrix[pos[k][0]][pos[k][1]] = t;
          t = temp;
        }
        matrix[pos[0][0]][pos[0][1]] = t;
      }
    }
  }
}

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