E. Coin Troubles 夜

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

思维很重要呀 原来是一个背包呀

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 MOD=1000000007;
const int N=305;
const int M=100005;
int a[N],next[N];
bool head[N];
int dp[M];
vector< vector<int> >h;
void packComplete(int cost,int V)
{
    for(int v=cost;v<=V;++v)
    dp[v]=(dp[v]+dp[v-cost])%MOD;
}
int main()
{
    //freopen("data.in","r",stdin);
    int n,q,t;
    while(cin>>n>>q>>t)
    {
        h.clear();
        memset(next,0,sizeof(next));
        for(int i=1;i<=n;++i)
        cin>>a[i];
        memset(head,true,sizeof(head));
        while(q--)
        {
            int l,r;
            cin>>l>>r;
            head[r]=false;
            next[l]=r;
        }
        int line[N],m;
        for(int i=1;i<=n;++i)
        if(head[i]==true)
        {
            int l=i;
            m=0;
            line[m++]=l;
            while(next[l]!=0)
            {
                l=next[l];
                line[m++]=l;
            }
            h.push_back(vector<int>(line,line+m));
        }
        int num=0;
        for(int unsigned i=0;i<h.size();++i)
        num+=h[i].size();
        if(num<n)
        {cout<<"0"<<endl;continue;}
        memset(dp,0,sizeof(dp));
        int V=t;
        int k=0;
        dp[0]=1;
        for(unsigned int i=0;i<h.size();++i)
        {
            int tmp=0;
            for(unsigned int j=0;j<h[i].size();++j)
            {
                int l=h[i][j];
                if(k<=V)
                k=k+(h[i].size()-1-j)*a[l];
                if(tmp>V) continue;
                tmp+=a[l];
                if(tmp<=V)
                packComplete(tmp,V);
            }
        }
        if(k>V)
        {cout<<"0"<<endl;continue;}
        cout<<dp[V-k]<<endl;
    }
    return 0;
}