poj 2686 Traveling by Stagecoach(状态压缩dp)

挑战程序设计竞赛里面的例题

#include <stdio.h>#include <string.h>#include <algorithm>using namespace std;const int INF = 0x3f3f3f3f;const int MAXN = 10;const int MAXM = 31;int n,m,p,a,b;int t[MAXN];//dp[S][v]:=到达剩下的车票集合为S并且现在在城市v的状态所需要的最小花费double dp[1<<MAXN][MAXM];int d[MAXM][MAXM];//邻接矩阵，-1表示没有边void solve(){    for(int i=0; i< (1<<n); i++)        fill(dp[i],dp[i]+m,INF);    dp[(1<<n)-1][a-1]=0;    double res=INF;    for(int S = (1<<n)-1; S >= 0; S--)    {        res=min(res,dp[S][b-1]);        for(int v = 0; v < m; v++)            for(int i = 0; i < n; i++)                if(S>>i&1)                    for(int u = 0; u < m; u++)                        if(d[v][u]>=0)                            dp[S&~(1<<i)][u]=min(dp[S&~(1<<i)][u],dp[S][v]+(double)d[v][u]/t[i]);    }    if(res==INF)        printf("Impossible\n");    else        printf("%.3f\n",res);}int main (){    while(scanf("%d%d%d%d%d",&n,&m,&p,&a,&b) && n+m+p+a+b)    {        memset(d,-1,sizeof(d));        for(int i=0; i<n; i++)            scanf("%d",&t[i]);        for(int i=0; i<p; i++)        {            int u,v,w;            scanf("%d %d %d",&u,&v,&w);            d[--u][--v] = w;            d[v][u] = w;        }        solve();    }    return 0;}