ACWing1133. 第二短路

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef pair<int,int> pii;
 4 const int N=1e5+5;
 5 int dis1[N],dis2[N],ans=INT_MAX;
 6 vector<pii>G[N];
 7 struct cmp
 8 {
 9   bool operator ()(pii &a,pii &b)
10     {
11       return a.second>b.second;
 
12     }
13 };
14 void dijkstra()
15 {
16   priority_queue<pii,vector<pii>,cmp>q;
17   q.push({1,0});
18   while(q.size())
19   {
20     auto p=q.top();
21     int u=p.first,d=p.second;
22     q.pop();
23     for(int i=0;i<G[u].size();i++)
24     {
25       int vv=G[u][i].first,w=G[u][i].second;
 
26       if(d+w<dis1[vv])
27       {
28         dis2[vv]=dis1[vv];
29         dis1[vv]=d+w;
30         q.push({vv,d+w});
31       }
32       else if(d+w>dis1[vv]&&d+w<dis2[vv])
33       {
34         dis2[vv]=d+w;
35         q.push({vv,d+w});
36       }
37     }
38     
39   }
40   
41
 
 }
42 int main()
43 {
44   int n,m;
45   scanf("%d%d",&n,&m);
46   memset(dis1,0x3f,sizeof(dis1));
47   memset(dis2,0x3f,sizeof(dis2));
48   for(int i=1;i<=m;i++)
49   {
50     int u,v,w;
51     scanf("%d%d%d",&u,&v,&w);
52     G[u].push_back({v,w});
53     G[v].push_back({u,w});
54   }
55   dijkstra();
56   cout<<dis2[n]<<endl;
57   return 0;
58 }