Codeforces 1084B. Kvass and the Fair Nut

n个杯子，里面各有a[i]升水，问是否能从中倒出来s升水，如果不能输出-1，否则输出剩下的各个杯子水中最小的升数。
一开始不用脑子从最小的开始枚举，一直到0，果然TLE。
然后果断二分，就Ac啦

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
LL n,s,a[1010],sum,mim = 0x3f3f3f3f,l,r,mid,ans; 
int can(LL x){
	return (sum-n*x>=s?1:0);
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	//freopen("data.in","r",stdin);
	//freopen("data.out","w",stdout);
	cin>>n>>s;
	for(int i = 1;i<=n;i++)	{
		cin>>a[i];
		sum += a[i]; 
		mim = min(mim,a[i]);
	}
	if(sum<s) {
		cout<<-1;return 0;
	}
	l = 0;r = mim;
	while(l<=r){
		mid = (l+r)>>1;//		cout<<l<<' '<<r<<' '<<mid<<endl;
		if(can(mid)) l = mid+1,ans = max(ans,mid);
		else r = mid-1; 
	}
	cout<<ans;
	return 0; 
}