Single source shortest path algorithm and priority_queue used to solve the problem.
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#include <iostream> #include <queue> #include <cstdio> #include <vector> #define INF 1000000000 #define ll long long using namespace std; /* struct node{ int dest,weight; }; */ int n,m,src,dst; vector<pair<int,int> > vb[20005]; void dijkstra(vector<ll> distance) { int t_dist,t_node; int latency,v; pair<int,int> _intPair; priority_queue<pair<int,int>,vector<pair<int,int> >, greater<pair<int,int> > > cue; cue.push(pair<int,int> (0,src)); pair<int,int> tmp; while(!cue.empty()) { tmp=cue.top(); cue.pop(); t_dist = tmp.first; t_node = tmp.second; if(t_dist==distance[t_node])//visited or discovered { for(int i=0;i<vb[t_node].size();i++) { _intPair = vb[t_node][i]; v = _intPair.first; latency = _intPair.second; if(t_dist+latency<distance[v]) { distance[v]=t_dist+latency; cue.push(make_pair(distance[v],v)); } } } } if(distance[dst]!=INF) printf("%lld\n",distance[dst]); else printf("unreachable\n"); } int main() { int t; int kase=1; int s,d,wt; scanf("%d",&t); while(t--) { scanf("%d%d%d%d",&n,&m,&src,&dst); for(int i=0;i<m;i++) { scanf("%d%d%d",&s,&d,&wt); vb[s].push_back(make_pair(d,wt)); vb[d].push_back(make_pair(s,wt)); } vector<ll> distance(n,INF); distance[src]=0; printf("Case #%d: ",kase++); dijkstra(distance); for(int i=0;i<n;i++) vb[i].clear(); } return 0; } |