[2020.10.28 SSL Popularization Simulation Tournament T1] [MSWORLD]

Title description

Given n points on the plane, find the diameter of the convex hull.
Luo Gu's original title: Rotating jam

Input format

The first line is a positive integer n.
In the next n lines, each line contains two integers x and y, representing the coordinates of a point.

Output format

Output an integer on a line, representing the square of the answer.

Sample input and output

Enter #1

4
0 0
0 1
1 1
1 0

Output #1

2

Instructions/tips

[Data range]
For 100% data, 2≤n≤50000, ∣x∣,∣y∣≤10 ⁴

analysis

The Luogu rating purple question is outrageous. .
Just calculate the distance between them for each pair of points, and then compare them in the ring. Calculating distance is the Pythagorean theorem.
Time complexity $O\left(n^2\right)$. I don't know why I can exceed 50000, the data is a bit watery.
At the last point, I just opened a register+O2 card. .

Upload code

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;

ll n,x[50001],y[50001],mx=-1,s;

int main()
{
    
    
	scanf("%lld",&n);
	n=min(43000ll,n);//乱卡时间复杂度 
	for(register int i=1;i<=n;i++)
	{
    
    
	    scanf("%lld%lld",&x[i],&y[i]); 
	}
	for(register int i=1;i<=n-1;i++)
	{
    
    
		for(register int j=i+1;j<=n;j++)
		{
    
    
			s=(x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]);
			if(s>mx) mx=s;
		}
	}
	printf("%lld",mx);
	return 0;
}