poj3411 Paid Roads

思路：

搜索。注意点和边都有可能经过多次。

实现：

 #include <iostream>
 #include <cstdio>
 #include <vector>
 using namespace std;
 const int MAXN = , INF = 0x3f3f3f3f;
 int n, m;
 struct edge
 {
     int to, c, p, r;
 };
 vector<edge> G[MAXN];
 int vis[MAXN];

 int dfs(int now)
 {
     if (now == n)
         return ;
     int ans = INF;
     for (int i = ; i < G[now].size(); i++)
     {
         if (vis[G[now][i].to] > ) continue;
         vis[G[now][i].to]++;
         int x = dfs(G[now][i].to) + G[now][i].r;
         ans = min(ans, x);
         int y = INF;
         if (vis[G[now][i].c])
             y = dfs(G[now][i].to) + G[now][i].p;
         ans = min(ans, y);
         vis[G[now][i].to]--;
     }
     return ans;
 }

 int main()
 {
     cin >> n >> m;
     int a, b, c, p, r;
     for (int i = ; i < m; i++)
     {
         cin >> a >> b >> c >> p >> r;
         G[a].push_back(edge{b, c, p, r});
     }
     vis[] = true;
     int ans = dfs();
     if (ans == INF) puts("impossible");
     else cout << ans << endl;
     return ;
 }