bzoj 2792: [Poi2012]Well【二分+贪心】

 #include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int N=1000005;
int n,a[N],b[N];
long long m,f[N],s[N];
int ok(int w)
{
    long long ans=0;
    for(int i=1;i<=n;i++)
		b[i]=a[i];
    for(int i=2;i<=n;i++)
		if(b[i]-b[i-1]>w)
			ans+=b[i]-b[i-1]-w,b[i]=b[i-1]+w;
    for(int i=n-1;i>=1;i--)
		if(b[i]-b[i+1]>w)
			ans+=b[i]-b[i+1]-w,b[i]=b[i+1]+w;
    for(int i=1;i<=n;i++)
		s[i]=s[i-1]+b[i];
    if(ans>m)
		return 0;
    for(int i=1,j=1;i<=n;i++)
    {
        while(j<i&&b[j]<=1ll*(i-j)*w)
			j++;
        f[i]=s[i-1]-s[j-1]-1ll*(i-j)*(i-j+1)/2*w;
    }
    for(int i=n,j=n;i;i--)
    {
        while(j>i&&b[j]<=1ll*(j-i)*w)
			j--;
        f[i]+=s[j]-s[i]-1ll*(j-i)*(j-i+1)/2*w;
    }
    for(int i=1;i<=n;i++)
		if(b[i]+f[i]+ans<=m)
			return i;
    return 0;
}
int main()
{
    int l=0,r=0,ans=0;
    scanf("%d%lld",&n,&m);
    for(int i=1;i<=n;i++)
    scanf("%d",&a[i]),r=max(r,a[i]);
    while(l<=r)
    {
		int mid=(l+r)>>1;
        if(ok(mid))
			r=mid-1,ans=mid;
        else
			l=mid+1;
    }
    printf("%d %d",ok(ans),ans);
	return 0;
}