48. Rotate Image 解题记录

题目描述：

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]
]

解题思路：

这题我的思路是把矩阵按一圈一圈来转，例如红色区域：

[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

就是一圈。

 

第二段代码是我在LeetCode上看到的优质解答，思路是：将一维数组反转，然后进行以左上到右下的数字进行轴对称。

我的代码：

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int times = matrix.size()/2, n = matrix.size();
        for(int i = 0; i <= times; i++){
            int tempTimes = n-2*i, nowTimes = 1, endIndex = n-1-i, begIndex = i;
            while(nowTimes++ < tempTimes){
                int t = matrix[i][begIndex];
                matrix[i][begIndex] = matrix[endIndex][i];
                matrix[endIndex][i] = matrix[n-1-i][endIndex];
                matrix[n-1-i][endIndex--] = matrix[begIndex][n-1-i];
                matrix[begIndex++][n-1-i] = t;
            }
        }
        return;
    }
};

他人代码：

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.size();j++){
                swap(matrix[i][j], matrix[j][i]);
            }
        }
    }
};