48. Rotate Image.md

48. Rotate Image

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Difficulty : Medium

Related Topics : Array

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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]]

Example 3:

Input: matrix = [[1]]
Output: [[1]]

Example 4:

Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]

Constraints:

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

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Solution

• mine
  • Java
    • Runtime: 0 ms, faster than 100.00%, Memory Usage: 38.9 MB, less than 49.76% of Java online submissions

      //O(N^2)time
      //O(1)space
      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[][] pos = new int[][]{{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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• the most votes

• Runtime: 0 ms, faster than 100.00%, Memory Usage: 39.2 MB, less than 49.76% of Java online submissions

  // O(N^2)time
  // O(1)space
  public void rotate(int[][] matrix) {
      for(int i = 0; i<matrix.length; i++){
          for(int j = i; j<matrix[0].length; j++){
              int temp = 0;
              temp = matrix[i][j];
              matrix[i][j] = matrix[j][i];
              matrix[j][i] = temp;
          }
      }
      for(int i =0 ; i<matrix.length; i++){
          for(int j = 0; j<matrix.length/2; j++){
              int temp = 0;
              temp = matrix[i][j];
              matrix[i][j] = matrix[i][matrix.length-1-j];
              matrix[i][matrix.length-1-j] = temp;
          }
      }
  }
  

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