D. Cow Program 夜

http://codeforces.com/contest/284/problem/D

dp+记忆化搜索

代码：

#include<iostream>
#include<cmath>
#include<cstdio>
#include<string>
#include<cstring>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<algorithm>

#define LL long long

using namespace std;

const int INF=0x3f3f3f3f;
const int N=200005;
long long inc[N],decr[N];
int had1[N],had2[N];
int a[N];
int n;
long long dpdecr(int x,int k);
long long dpinc(int x,int k)
{//cout<<"inc "<<x<<" "<<k<<endl;
    if(x<=0||x>n)
    return 0;
    if(had1[x]==k)
    return -1;
    if(inc[x]!=-2)
    return inc[x];
    had1[x]=k;
    long long tmp=dpdecr(x+a[x],k);
    if(tmp==-1)
    return (inc[x]=-1);
    return (inc[x]=tmp+a[x]);
}
long long dpdecr(int x,int k)
{//cout<<"decr "<<x<<" "<<k<<endl;
    if(x<=0||x>n)
    return 0;
    if(had2[x]==k)
    return -1;
    if(decr[x]!=-2)
    return decr[x];
    had2[x]=k;
    long long tmp=dpinc(x-a[x],k);
    if(tmp==-1)
    return (decr[x]=-1);
    return (decr[x]=tmp+a[x]);
}
int main()
{
    //freopen("data.in","r",stdin);
    while(cin>>n)
    {
        for(int i=2;i<=n;++i)
        cin>>a[i];
        memset(had1,0,sizeof(had1));
        memset(had2,0,sizeof(had2));
        for(int i=1;i<=n;++i)
        inc[i]=decr[i]=-2;
        inc[1]=-1;
        decr[1]=0;
        for(int i=2;i<=n;++i)
        {
           long long k=dpdecr(i,i);
           if(k==-1)
           cout<<"-1"<<endl;
           else
           cout<<(k+i-1)<<endl;
        }
    }
    return 0;
}