HDU 2647 Reward【拓扑排序】

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring> 
 4 #include <cmath> 
 5 #include<stack>
 6 #include<vector>
 7 #include<map> 
 8 #include<set>
 9 #include<queue> 
10 #include<algorithm>  
11 using namespace std;
12 
13 #define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)
14 
15 typedef long long LL;
16 const int INF = (1<<30)-1;
17 const int mod=1000000007;
18 const int maxn=100005;
19 
20 int ans[maxn],nextt[maxn],firstt[maxn],in[maxn],e[maxn],money[maxn];
21 int n,m,ecnt;
22 int tot;
23 
24 void toposort(){
25     queue<int> q;
26     for(int i=1;i<=n;i++)
27     if(in[i]==0) q.push(i);
28     
29     tot=0;
30     int cnt=0;
31     while(!q.empty()){
32         int tmp=q.front();q.pop();
33         ans[++cnt]=tmp;
34         tot+=money[tmp];
35         
36             for(int k=firstt[tmp];k!=-1;k=nextt[k]){
37                 in[e[k]]--;
38                 if(in[e[k]]==0) {
39                     money[e[k]]=money[tmp]+1;
40                     q.push(e[k]);
41                 }
42             }                    
43     }
44     
45     if(cnt==n) printf("%d\n",tot);
46     else printf("-1\n");
47 }
48 
49 void addedges(int u,int v){
50     e[++ecnt]=v;
51     nextt[ecnt]=firstt[u];
52     firstt[u]=ecnt;        
53     in[v]++;
54 }
55 
56 
57 int main(){
58     while(scanf("%d %d",&n,&m)!=EOF){
59         
60         ecnt=0;
61         memset(in,0,sizeof(in));                
62         memset(firstt,-1,sizeof(firstt));
63         for(int i=1;i<=n;i++) money[i]=888;
64         
65         while(m--){
66             int u,v;
67             cin>>u>>v;
68             addedges(v,u);            
69         }
70         toposort();
71     }
72     return 0;
73 }