spfa 

 1 /*
 2   题意：最短路
 3   思路：spfa
 4   时间：2018.07.18
 5 */
 6 #include <bits/stdc++.h>
 7 using namespace std;
 8 
 9 typedef long long LL;
10 const int MAXN=100005;
11 const LL MOD7 = 1e9+7;
12 
13 struct Edge
14 {
15     int u,v,c;
16     int next;
17 }edge[2*MAXN];
18 int head[MAXN];
19 int cnt;
20 
21 int dis[MAXN];
22 int vis[MAXN];
23 int num[MAXN];
24 int n,m;
25 
26 void init()
27 {
28     cnt=0;
29     memset(head,-1,sizeof(head));
30 }
31 
32 void addEdge(int u,int v,int c)
33 {
34     edge[cnt].u=u;edge[cnt].v=v;edge[cnt].c=c;edge[cnt].next=head[u];head[u]=cnt++;
35 }
36 
37 void spfa(int st,int et)
38 {
39     queue<int> q;
40     memset(vis,0,sizeof(vis));
41     memset(dis,-1,sizeof(dis));
42     memset(num,0,sizeof(num));
43     while (!q.empty()) q.pop();
44     q.push(st);
45     dis[st]=0;
46     vis[st]=1;
47     num[st]=1;
48     while (!q.empty())
49     {
50         int u=q.front();q.pop();
51         // if (u==et) break;
52         vis[u]=0;
53         for (int i=head[u];i!=-1;i=edge[i].next)
54         {
55             int v=edge[i].v;
56             int c=edge[i].c;
57             if (dis[v]==-1 || dis[u]+c<dis[v])
58             {
59                 dis[v]=dis[u]+c;
60                 if (!vis[v])
61                 {
62                     vis[v]=1;
63                     q.push(v);
64                     if (++num[v]>n) break;
65                 }
66             }
67         }
68     }
69     printf("%d\n",dis[et]);
70 }
71 
72 int main()
73 {
74 #ifndef ONLINE_JUDGE
75     freopen("test.txt","r",stdin);
76 #endif // ONLINE_JUDGE
77     int st,et;
78     scanf("%d%d",&n,&m);
79     scanf("%d%d",&st,&et);
80     init();
81     int u,v,c;
82     for (int i=1;i<=m;++i)
83     {
84         scanf("%d%d%d",&u,&v,&c);
85         addEdge(u,v,c);
86         addEdge(v,u,c);
87     }
88     spfa(st,et);
89     return 0;
90 }

 

posted @ 2018-07-18 23:09  LeeSongt  阅读(212)  评论(0)    收藏  举报