二分答案AC

#include<bits/stdc++.h>
using namespace std;
const int N = 1e6+10;
long long a[N];
long long n,m,mx=0,ans=0;
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		mx = max(mx,a[i]);
	}
	int l = 0,r = mx;
	while(l<=r){
		int mid = (l+r)/2;
		long long sum = 0;
		for(int i=1;i<=n;i++){
			if(a[i] > mid){
				sum += a[i] - mid;
			}
		}
		if(sum >= m){
			l = mid+1;
			ans = mid;
		}
		else{
			r = mid - 1;
		}
	}
	cout<<ans;
	
	return 0;
}