leetcode 48. Rotate image

leetcode 48. Rotate image

Question stem

Given an n × n two-dimensional matrix represents an image.
Rotate the image 90 degrees clockwise.

Note:
You must rotate the image in place, which means you need to directly modify the input two-dimensional matrix. Please do not use another matrix to rotate the image.

Example 1:
Given matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
rotate the input matrix in place to make it:
[
[7,4, 1],
[8,5,2],
[9,6,3]
]

Example 2:
Given matrix =
[
[5, 1, 9,11],
[2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
], the
original Rotate the input matrix so that it becomes:
[
[15,13, ​​2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]

answer

Flip step by step from the outside to the inside, flip one circle of the square at a time, pay attention to the exchange and coverage of elements

class Solution {
    
    
public:
    void rotate(vector<vector<int>>& matrix) {
    
    
        int n = matrix.size();
        if(n == 1){
    
    
            return;
        }
        int head,tail;
        //按圈遍历，从外到内
        for(int i = 0 ; i <= n / 2 ; ++i){
    
    
            head = i;
            tail = n - 1 - i;
            //(0,2) <- (2,0)
            //从左上角开始交换,起始坐标(i,head)
            while(head < tail){
    
    
                //cout<<"("<<i<<","<<head<<")"<<endl;
                int preValue = matrix[n - 1 - head][i];
                int nowRowIndex = i;
                int nowColIndex = head;
                for(int j = 0 ; j < 4 ; ++j){
    
    
                    int temp = matrix[nowRowIndex][nowColIndex];
                    matrix[nowRowIndex][nowColIndex] = preValue;
                    preValue = temp;
                    temp = nowColIndex;
                    nowColIndex = n - 1 - nowRowIndex;
                    nowRowIndex = temp;
                }
                head++;
            }
        }
        return;
    }
};

Another method is to first transpose and then flip horizontally. If you want to report, you can implement it without writing code.