hdu_6047: Maximum Sequence (2017 多校第二场 1003）【贪心】

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

const int N=3e5+7;
const int mod=1e9+7;

int n;
int a[N],b[N],c[N];

int main()
{
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++) scanf("%d",&a[i]);
        for(int i=1;i<=n;i++) scanf("%d",&b[i]);
        sort(b+1,b+1+n);
        c[n]=a[n]-n;
        for(int i=n-1;i>0;i--) c[i]=max(c[i+1],a[i]-i);
        //c[i]:  max{a[j]-j| i<=j<=n}
        LL ans=0;
        int ma=-mod;
        //ma: max{a[j]-j| n<j<n+i
        for(int i=1;i<=n;i++)
        {
            int t=max(c[b[i]],ma);    //t: a[n+i]
            ma=max(ma,t-(n+i));        //a[n+i] in,update ma 
            ans=(ans+t)%mod;    
        }
        printf("%lld\n",ans);
    }
}