51nod 1443 路径和树(单元最短路径)

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<queue>
 5 #include<vector>
 6 #include<algorithm>
 7 using namespace std;
 8 typedef long long ll;
 9 const int maxn=3e5+5;
10 const ll inf=1e18;
11 struct Edge{
12     int u,v;
13     ll w;
14     Edge(int _u,int _v,ll _w):u(_u),v(_v),w(_w){}
15 };
16 bool Cmp(Edge a,Edge b){
17     return a.w<b.w;
18 }
19 vector<Edge> edges;
20 vector<int>G[maxn];
21 void AddEdge(int u,int v,ll w){
22     edges.push_back(Edge(u,v,w));
23     edges.push_back(Edge(v,u,w));
24     G[u].push_back(edges.size()-2);
25     G[v].push_back(edges.size()-1);
26 }
27 
28 int u,n,m;
29 ll dis[maxn];
30 ll pre[maxn];
31 bool inq[maxn];
32 void spfa(){
33     memset(inq,0,sizeof(inq));
34     memset(pre,0,sizeof(pre));
35     for(int i=1;i<=n;i++)dis[i]=inf;
36     queue<int> Q;
37     Q.push(u);
38     inq[u]=true;
39     dis[u]=0;
40     while(!Q.empty()){
41         int x=Q.front();Q.pop();
42         inq[x]=false;
43         for(int i=0;i<G[x].size();i++){
44             Edge &e=edges[G[x][i]];
45             if(dis[e.v]>dis[e.u]+e.w){
46                 dis[e.v]=dis[e.u]+e.w;
47                 pre[e.v]=e.w;
48                 if(!inq[e.v]){inq[e.v]=true;Q.push(e.v);}
49             }
50             else if(dis[e.v]==dis[e.u]+e.w)pre[e.v]=min(pre[e.v],e.w);
51         }
52     }
53 }
54 int main(){
55 //    freopen("e:\\in.txt","r",stdin);
56     int from,to;
57     ll weight;
58     scanf("%d%d",&n,&m);
59     for(int i=0;i<m;i++){
60         scanf("%d%d%lld",&from,&to,&weight);
61         AddEdge(from,to,weight);
62     }
63     scanf("%d",&u);
64     spfa();
65     ll ans=0;
66     for(int i=1;i<=n;i++){
67         ans+=pre[i];
68     }
69     printf("%lld\n",ans);
70     return 0;
71 }