[Swust OJ 582]--放学了,抢机子了(SPFA)

 1 #include <iostream>
 2 #include <queue>
 3 #include <vector>
 4 #include <cstring>
 5 using namespace std;
 6 
 7 #define maxn  10005
 8 #define inf 0x3f3f3f3f
 9 
10 struct node{
11     int v, w;
12     node(int x, int y) :v(x), w(y){};
13     node(){};
14 };
15 
16 vector<node>mpt[maxn];
17 //ptr判断一个点的入队操作次数,判断负环
18 int vis[maxn], ptr[maxn], dis[maxn], t, n, m, u, v, w, s;
19 
20 int Spfa(int s){
21     queue<int>Q;
22     Q.push(s);
23     vis[s] = 1, dis[s] = 0, ptr[s] = 1;
24     while (!Q.empty()){
25         int u = Q.front();
26         Q.pop();
27         vis[u] = 0;
28         for (int i = 0; i<mpt[u].size(); i++){
29             v = mpt[u][i].v;
30             if (dis[v]>dis[u] + mpt[u][i].w){
31                 dis[v] = dis[u] + mpt[u][i].w;
32                 if (!vis[v]){
33                     vis[v] = 1;
34                     Q.push(v);
35                     if (++ptr[v] > n) return 0;
36                 }
37             }
38         }
39     }
40     return 1;
41 }
42 
43 int main(){
44     while (cin >> n >> m){
45         memset(vis, 0, sizeof(vis));
46         memset(dis, inf, sizeof(dis));
47         memset(ptr, 0, sizeof(ptr));
48         for (int i = 0; i < m; i++){
49             cin >> u >> v >> w;
50             mpt[u].push_back(node(v, w));
51         }
52         cin >> s >> t;
53         if (Spfa(s))
54             cout << dis[t] << endl;
55         else
56             cout << "No Solution!\n";
57     }
58     return 0;
59 }