NOIP 2014 Day2 T2 寻找道路

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<queue>
 5 #include<stack>
 6 #include<vector>
 7 #include<algorithm>
 8 #include<string>
 9 #include<cstring>
10 #include<iomanip>
11 #include<bitset>
12 #include<cstdlib>
13 using namespace std;
14 vector <int> f[10005],g[10005];
15 queue <int> q;
16 int n,m,a,b,s,t,maxn;
17 int dis[10005];
18 bool vis[10005],del[10005],iin[10005],dee[10005];
19 void deletee(int x)
20 {
21     del[x]=false;
22     for (int i=0;i<g[x].size();i++)
23         if (del[g[x][i]])//here
24             deletee(g[x][i]);
25 }
26 void sp()
27 {
28     for (int i=1;i<=n;i++)
29         if (del[i])
30             for (int j=0;j<g[i].size();j++)
31                 dee[g[i][j]]=true;
32     for (int i=1;i<=n;i++)
33         dee[i]=dee[i]|del[i];
34 }
35 void spfa()
36 {
37     memset(dis,127,sizeof(dis));
38     dis[s]=0;
39     q.push(s);
40     iin[s]=true;
41     while (!q.empty())
42     {
43         int k=q.front();q.pop();iin[k]=false;
44         for (int i=0;i<f[k].size();i++)
45             if (!dee[f[k][i]]&&dis[k]+1<dis[f[k][i]])
46             {
47                 dis[f[k][i]]=dis[k]+1;
48                 if (!iin[f[k][i]])
49                 {
50                     q.push(f[k][i]);
51                     iin[f[k][i]]=true;
52                 }
53             }
54     }
55 }
56 int main()
57 {
58     freopen ("road.in","r",stdin);
59     //freopen ("road.out","w",stdout);
60     scanf ("%d%d",&n,&m);
61     for (int i=1;i<=m;i++)
62     {
63         scanf ("%d%d",&a,&b);
64         if (a!=b)
65         {
66             f[a].push_back(b);
67             g[b].push_back(a);
68         }
69     }
70     scanf ("%d%d",&s,&t);
71     memset(del,true,sizeof(del));
72     deletee(t);sp();
73     spfa();
74     if (dis[t]>100000)  printf ("-1");
75     else printf ("%d",dis[t]);
76     return 0;
77 }