BZOJ1674: [Usaco2005]Part Acquisition

 1 #include<cstdio>
 2 #include<cstdlib>
 3 #include<cmath>
 4 #include<cstring>
 5 #include<algorithm>
 6 #include<iostream>
 7 #include<vector>
 8 #include<map>
 9 #include<set>
10 #include<queue>
11 #define inf 1000000000
12 #define maxn 50000+100
13 #define maxm 2000000
14 #define eps 1e-10
15 #define ll long long
16 #define pa pair<int,int>
17 using namespace std;
18 inline int read()
19 {
20     int x=0,f=1;char ch=getchar();
21     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
22     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}
23     return x*f;
24 }
25 int n,m,tot;
26 int d[1005],head[1005];
27 bool v[1005];
28 struct edge{int go,next,w;}e[50005];
29 void insert(int x,int y,int z)
30 {
31     e[++tot].go=y;e[tot].w=z;e[tot].next=head[x];head[x]=tot;
32 }
33 void dijkstra()
34 {
35     priority_queue<pa,vector<pa>,greater<pa> >q;
36     for(int i=1;i<=n;i++)d[i]=inf;
37     memset(v,0,sizeof(v));
38     d[1]=0;q.push(make_pair(0,1));
39     while(!q.empty())
40     {
41         int x=q.top().second;q.pop();
42         if(v[x])continue;v[x]=1;
43         for(int i=head[x],y;i;i=e[i].next)
44             if(d[x]+e[i].w<d[y=e[i].go])
45             {
46                 d[y]=d[x]+e[i].w;
47                 q.push(make_pair(d[y],y));
48             }
49         
50     }
51 }
52 int main()
53 {
54     freopen("input.txt","r",stdin);
55     freopen("output.txt","w",stdout);
56     m=read();n=read();
57     for(int i=1;i<=m;i++)
58     {
59         int x=read(),y=read(),z=1;
60         insert(x,y,z);
61     }
62     dijkstra();
63     if(d[n]==inf)puts("-1");
64     else printf("%d",d[n]+1);
65     return 0;
66 }