POJ 2686 Traveling by Stagecoach 状态DP

水深无声 2021-12-21 00:27 186阅读 0赞

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//#pragma comment(linker, "/STACK:1024000000,1024000000")
    #include<cstdio>
    #include<cstring>
    #include<cstdlib>
    #include<algorithm>
    #include<iostream>
    #include<sstream>
    #include<cmath>
    #include<climits>
    #include<string>
    #include<map>
    #include<queue>
    #include<vector>
    #include<stack>
    #include<set>
    using namespace std;
    typedef long long ll;
    typedef unsigned long long ull;
    typedef pair<int,int> pii;
    #define pb(a) push(a)
    #define INF 0x1f1f1f1f
    #define lson idx<<1,l,mid
    #define rson idx<<1|1,mid+1,r
    #define PI  3.1415926535898
    template<class T> T min(const T& a,const T& b,const T& c) {
        return min(min(a,b),min(a,c));
    }
    template<class T> T max(const T& a,const T& b,const T& c) {
        return max(max(a,b),max(a,c));
    }
    void debug() {
    #ifdef ONLINE_JUDGE
    #else
    
        freopen("d:\\in1.txt","r",stdin);
        freopen("d:\\out1.txt","w",stdout);
    #endif
    }
    int getch() {
        int ch;
        while((ch=getchar())!=EOF) {
            if(ch!=' '&&ch!='\n')return ch;
        }
        return EOF;
    }
    
    double dp[33][1<<8];
    int t[8];
    int g[33][33];
    int n,m,p,a,b;
    int read()
    {
        scanf("%d%d%d%d%d",&n,&m,&p,&a,&b);
        if(n==0)return 0;
        for(int i=0;i<n;i++)
            scanf("%d",&t[i]);
        memset(g,-1,sizeof(g));
        for(int i=1;i<=p;i++)
        {
            int u,v,w;
            scanf("%d%d%d",&u,&v,&w);
            g[u][v]=g[v][u]=w;
        }
        return 1;
    }
    double dfs(int u,int k,int st)
    {
        if(u==b)return 0;
        if(dp[u][st]>=0)return dp[u][st];
        if(k==n)return INF;
        double &ans=dp[u][st];
        ans=INF;
        for(int i=1;i<=m;i++)if(g[u][i]!=-1)
        {
            for(int j=0;j<n;j++)if(!(st&(1<<j)))
            {
                ans=min(ans,(double)g[u][i]/t[j]+dfs(i,k+1,st|(1<<j)));
            }
        }
        return ans;
    }
    int main()
    {
        while(read())
        {
            memset(dp,-1,sizeof(dp));
            double res=dfs(a,0,0);
            if(res>=INF)printf("Impossible\n");
            else printf("%lf\n",res);
        }
        return 0;
    }

转载于:https://www.cnblogs.com/BMan/p/3595226.html

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