POJ 3411 Paid Roads(DFS)

题目链接

点和边 都很少，确定一个界限，爆搜即可。判断点到达注意一下，如果之前已经到了，就不用回溯了，如果之前没到过，要回溯。

 #include <cstring>
 #include <cstdio>
 #include <string>
 #include <iostream>
 #include <algorithm>
 #include <vector>
 #include <queue>
 using namespace std;
 struct node
 {
     int a,b,c,p,r,next;
 } edge[];
 int first[],t,minz;
 int o[],n;
 void CL()
 {
     t = ;
     memset(first,-,sizeof(first));
     memset(o,,sizeof(o));
 }
 void add(int a,int b,int c,int p,int r)
 {
     edge[t].a = a;
     edge[t].b = b;
     edge[t].c = c;
     edge[t].p = p;
     edge[t].r = r;
     edge[t].next = first[a];
     first[a] = t ++;
 }
 void dfs(int x,int sum)
 {
     int i,v,s,z;
     if(sum >= minz)
         return ;
     if(x == n)
     {
         minz = min(sum,minz);
         return ;
     }
     for(i = first[x]; i != -; i = edge[i].next)
     {
         v = edge[i].b;
         s = edge[i].c;
         z = ;
         if(o[s])
         {
             if(o[v])
             z = ;
             else
             o[v] = ;
             dfs(v,sum+edge[i].p);
             if(z == )
             o[v] = ;
         }
         else
         {
             if(o[v])
             z = ;
             else
             o[v] = ;
             dfs(v,sum+edge[i].r);
             if(z == )
             o[v] = ;
         }
     }
     return ;
 }
 int main()
 {
     int i,m,sum;
     int a,b,c,p,r;
     scanf("%d%d",&n,&m);
     CL();
     sum = ;
     for(i = ; i <= m; i ++)
     {
         scanf("%d%d%d%d%d",&a,&b,&c,&p,&r);
         add(a,b,c,p,r);
         sum += r;
     }
     minz = sum+;
     o[] = ;
     dfs(,);
     if(minz == sum+)
         printf("impossible\n");
     else
         printf("%d\n",minz);
     return ;
 }