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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]
    ]
    
    Accepted
    302,636
    Submissions
    589,748
     
     
    /*
     * clockwise rotate
     * first reverse up to down, then swap the symmetry 
     * 1 2 3     7 8 9     7 4 1
     * 4 5 6  => 4 5 6  => 8 5 2
     * 7 8 9     1 2 3     9 6 3
    */
    先按行上限翻转, 第1行和最后一行交换, 第i行和第n-i行交换
    然后再按对角线交换...惊呆了
    class Solution {
    public:
        void rotate(vector<vector<int>>& matrix) {
            reverse(matrix.begin(),matrix.end());
            for(int i=0;i<matrix.size();++i)
                for(int j=i+1;j<matrix[0].size();++j)
                    swap(matrix[i][j],matrix[j][i]);
        }
    };
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  • 原文地址:https://www.cnblogs.com/lychnis/p/11749147.html
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