萌新，只会暴力，70分代码，3个TLE

#include<bits/stdc++.h>
using namespace std;


int a[200000];
bool b[200000] = {0};
int c[200000];
int main()
{
	int n;
	int max = - 1;
	int xia = 1;
	int num = 0;
	cin >> n;
	for(int i = 1;i <= n;i++)
	{
		cin >> a[i];
	}
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= n;j++)
		{
			if(i != j)
			{
				if(b[a[i] % a[j]] != 1)
				{
					b[a[i] % a[j]] = 1;
					num++;
					if(a[i] % a[j] > max)
					{
						max = a[i] % a[j];
					}
			  }
			}
		}
	}
	if(num <= 2)
	{
		cout << -1 << endl;
	}
	else
	{
		for(int i = max - 1;i >= 1;i--)
		{
			if(b[i] == 1)
			{
				cout << i << endl;
				break;
			}
		}
	}
	return 0;
}