不懂题解

#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm> 
using namespace std;

const int N=500005;
int n, k, i, j; 
long long hp[N], Dmg[N], ans; 

bool check(long long p)
{
	long long used=0, i, j;
	memset(Dmg, 0, sizeof(Dmg));
	//cout<<p<<endl;
	for(i=1ll*n; i>=1ll; i--)
	{
		//int x=used;
		if(Dmg[i]>hp[i]) continue;
		used+=(hp[i]-Dmg[i])/p+1;
		//if(used!=x) cout<<Dmg[i]<<endl;
		for(j=i-1; j>=1&&(p-(i-j)*(i-j))>0; j--) 
			Dmg[j]+=((hp[i]-Dmg[i])/p+1) * max(0*1ll, p-1ll*(i-j)*(i-j));	
	}
	//cout<<used<<" ";
	return used<=(1ll*k);
}

int main()
{
	freopen("MianBao.in","r",stdin);
	cin>>n>>k;
	for(int i=1; i<=n; i++)
		scanf("%lld", &hp[i]);
	//cout<<mx<<endl; 
	long long l=1, r=1000000000000000, mid;
    while(l<r)
    {
        mid=(l+r)>>1;
        if(check(mid)) r=mid;
        else l=mid+1;
    }
    cout<<l<<endl;
	return 0;
}

//-1 0 -1 -2 -3 -2 -1 -2 -3