【LeetCode】48. Rotate Image (2 solutions)

Rotate Image

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

Rotate the image by 90 degrees (clockwise).

Follow up: Could you do this in-place?

最简单的想法，两重循环。

第一重循环是对于矩阵的层次（从外到内）

第二重循环是对于每一层次的四元素轮换

举例：

1 2 3

4 5 6

7 8 9

最外层：

1-->3-->9-->7

2-->6-->8-->4

最内层：

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

还有一种技巧性比较强的解法。

顺时针旋转90度可以分解为两步：

1、上下颠倒reverse

2、转置transpose

举例：

1 2 3

4 5 6

7 8 9

reverse之后

7 8 9

4 5 6

1 2 3

transpose之后

7 4 1

8 5 2

9 6 3

class Solution {
public:void rotate(vector<vector<int> > &matrix) {if(matrix.empty() || matrix[0].empty())return;reverse(matrix.begin(), matrix.end());int m = matrix.size();int n = matrix[0].size();for(int i = 0; i < m; i ++){for(int j = i+1; j < n; j ++){swap(matrix[i][j], matrix[j][i]);}}}
};

转载于:https://www.cnblogs.com/ganganloveu/p/3758105.html

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