【bzoj4412】[Usaco2016 Feb]Circular Barn

先看成一条链

for一遍找位置

在for一遍算答案

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

typedef long long LL;

#define N 100010

int n;
int cnt=1;

int a[N<<2],s[N<<2];

int main()
{
    freopen("a.in","r",stdin);freopen("a.out","w",stdout);
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
        scanf("%d",&a[i]),a[n+i]=a[i];
    for (int i=1;i<=n*2;i++)
    {
        if (i==cnt+n)
            break;
        s[i]=s[i-1]+a[i]-1;
        while (s[i]<s[cnt-1])
            cnt++;
    }
    LL ans=0;
    int l=cnt+n-1,r=cnt+n-1;
    while (r>=cnt)
    {
        while (!a[l]) 
            l--;
        ans+=(LL)(r-l)*(r-l);
        a[l]--;
        r--;
    }
    printf("%lld
",ans);
    return 0;
}