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  • 48. Rotate Image

    You are given an n x n 2D matrix representing an image.

    Rotate the image by 90 degrees (clockwise).

    Note:

    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:

    Given input matrix = 
    [
      [1,2,3],
      [4,5,6],
      [7,8,9]
    ],
    
    rotate the input matrix in-place such that it becomes:
    [
      [7,4,1],
      [8,5,2],
      [9,6,3]
    ]
    

    Example 2:

    Given input matrix =
    [
      [ 5, 1, 9,11],
      [ 2, 4, 8,10],
      [13, 3, 6, 7],
      [15,14,12,16]
    ], 
    
    rotate the input matrix in-place such that it becomes:
    [
      [15,13, 2, 5],
      [14, 3, 4, 1],
      [12, 6, 8, 9],
      [16, 7,10,11]
    ]
    首先我想说,leetcode上的大神真实他妈的宇宙无敌超级他妈的几把厉害,哦也可能是我太菜
    先交换行,再转置(两个可以交换顺序),就完成90度旋转了,真他妈的厉害。把我这个菜逼看的一愣一愣的
    class Solution {
        public void rotate(int[][] matrix) {
            /*1. 先交换行(先转置再交换列也行,但交换列对java不友好)
              2. 再转置
            */
            if(matrix.length<=1) return;
             int n = matrix.length;
            /*  1,2,3
                4,5,6
                7,8,9
            */
            for(int i=0;i<n/2;i++){
                int[] temp = matrix[i];
                matrix[i] = matrix[n-1-i];
                matrix[n-1-i] = temp;
            }
            /*  7,8,9
                4,5,6
                1,2,3
            */
            
            for(int i=0;i<n;i++){
                for(int j=i;j<n;j++){
                    int temp =  matrix[j][i];
                    matrix[j][i] = matrix[i][j];
                    matrix[i][j] = temp;
    
                }
            }
            /*  7,4,1
                8,5,2
                9,6,3
            */  
        }
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  • 原文地址:https://www.cnblogs.com/wentiliangkaihua/p/10341704.html
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