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  • Rotate image

    1.顺时针:

    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]
    ]
    class Solution {
    public:
        void rotate(vector<vector<int>>& matrix) {
            int n = matrix.size();
            if (n < 2) return;
         // 对行进行翻转 reverse(matrix.begin(),matrix.end());
    for (int i = 0; i < n; ++i) { for (int j = i + 1;j < n;++j) { swap(matrix[i][j],matrix[j][i]); } } } };

    2.逆时针

    class Solution {
    public:
        void rotate(vector<vector<int>>& matrix) {
            int n = matrix.size();
            if (n < 2) return;
         // 对列进行翻转
            for (auto vi: matrix)
                reverse(vi.begin(),vi.end());
            for (int i = 0; i < n; ++i)
            {
                for (int j = i + 1;j < n;++j)
                {
                    swap(matrix[i][j],matrix[j][i]);
                }
            }
        }
    };
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  • 原文地址:https://www.cnblogs.com/qiang-wei/p/11938143.html
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