LeetCode 48：旋转图像（Rotate Image）解法汇总

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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]
]

Solution

鉴于in-place的要求，所以不能allocate一个同样大小的数组。然而我还是使用了额外的空间，不知道是否符合题意。

采用的是一个链式的替换规则。

用箭头尾部的元素替代头部的元素。

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        for(int j = 0;j<matrix.size()/2;j++){
            for(int i = j;i<matrix.size()-1-j;i++) {
                int m = matrix.size() - 1 - i;
                int n = j;
                int temp = matrix[j][i];
                matrix[j][i] = matrix[m][n];
                while (!(matrix.size() - 1 - n == j && m == i)) {
                    matrix[m][n] = matrix[matrix.size() - 1 - n][m];
                    int t = n;
                    n = m;
                    m = matrix.size() - 1 - t;
                }
                matrix[m][n] = temp;
            }
        }
    }
};