P1873 二分答案 WA 9个点 求教

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

#define RE register
#define ll long long

ll n,m,imax=-233333333333;
ll f[1000100];

inline void fread(ll &x){
	x=0;
	ll f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		x=(x<<1)+(x<<3)+(ch^48);
		ch=getchar();
	}
	x*=f;
}

inline ll work(ll x){
	//cout<<x<<endl;
	ll ans=0;
	for(RE ll i=1;i<=n;i++){
		if(f[i]>x){
			ans+=f[i]-x;
		}
	}
	return ans;
}

int main(){
    freopen("P1863.in","w",stdin);
	fread(n);
	fread(m);
	for(RE ll i=1;i<=n;i++){
		fread(f[i]);
		imax=max(f[i],imax);
	}
	ll l=0,r=imax;
	while(l<=r){
		ll mid=(l+r)/2;
		ll t=work(mid);
		if(t>m){
			l=mid+1;
		}else if(t<m){
			r=mid-1;
		}else if(t==m){
			l=mid;
			break;
		}
	}
	cout<<l<<endl;
	return 0;
}