The point rotates clockwise around the center of the grid by 90 ° 180 ° 270 ° coordinate change

Record the conclusion directly ：s[i][j] ( The coordinates are from 0 At the beginning )

                     s[j][n - i - 1](90°)

                     s[n - j - 1][i](270°)

                     s[n - i - 1][n - j - 1](180°)

  Put an example for everyone and myself to understand

Codeforces Round #806 (Div. 4) E. Mirror Grid 

#include<bits/stdc++.h>

using namespace std;

int main()
{
	int t;
	cin >> t;
	while(t --)
	{
		int n;
		cin >> n;
		string s[n + 10];
		for(int i = 0; i < n; i ++)
		{
			cin >> s[i];
		}
		int ans = 0;
		for(int i = 0; i < n; i ++)
		{
			for(int j = 0; j < n; j ++)
			{
					int s0 = 0;
					int s1 = 0;
					if(s[i][j] == '0') s0 ++;
					else s1 ++;
					if(s[j][n - i - 1] == '0') s0 ++;
					else s1 ++;
					if(s[n - j - 1][i] == '0') s0 ++;
					else s1 ++;
					if(s[n - i - 1][n - j - 1] == '0') s0 ++;
					else s1 ++; 
				ans += min(s1, s0);( Each one finds the corresponding ones , have a look 1 Less or 0 Less , Less )
			}
		}
		cout << ans / 4 ( Because each one has been traversed , So I repeat 3 All over , Divide by 4)<< "\n";
	}
}

  Make a record of the questions ： The foundation is still too unsound , Many things are the first time to see , Start with this question , At first, I thought it was rotation 180°, Later, it was found that the sample was wrong , Only to find that it's not just this , A lot of time was wasted , Start to change again , Then I don't know how to do this , I may not know this conclusion , I hope I can keep this conclusion in mind , It can be used at a critical time in the future .