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  • leetcode 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]
    ]
    

    模拟一下,先看四个角,每次交换两个,交换三次就可以了。对于左上角向下走一个单位找到a,左下角向右移动一个单位b,右下角向上移动c,右上角向左移动d。交换(a,b)(b,c),(c,d)....
    具体见代码:

    class Solution {
    public:
        void rotate(vector<vector<int>>& matrix) {
            int n = matrix.size();
            if (n == 0) return ;
            int x = n/2;
            int y = n;
            for (int p = 0; p < x; ++p) {
                for (int i = 0; i <= y - 2; ++i) {
                    swap(matrix[p+i][p], matrix[n-p-1][p+i]);
                    swap(matrix[n-p-1][p+i], matrix[n-p-1-i][n-p-1]);
                    swap(matrix[n-p-1-i][n-p-1], matrix[p][n-p-1-i]);
                }
                y -= 2;
            }
        }
    };
    
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  • 原文地址:https://www.cnblogs.com/pk28/p/7714637.html
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