题目：https://ac.nowcoder.com/acm/contest/7830/B
n和m都很少，可以1e4次建图+dij暴力算期望
1 #include<bits/stdc++.h> 2 using namespace std; 3 typedef long long ll; 4 typedef unsigned long long ull; 5 //typedef __int128_t LL; 6 typedef double db; 7 #define rep(a,b,c) for(ll a=b;a<=c;a++) 8 #define per(a,b,c) for(ll a=b;a>=c;a--) 9 #define go(a,b) for(ll a=head[b];a;a=e[a].to) 10 #define endl ' ' 11 #define V vector 12 #define pb push_back 13 #define mp make_pair 14 #define mem(a,b) memset(a,b,sizeof(a)) 15 const ll amn=1e5+5,mod=1e9+7,inf=0x3f3f3f3f; 16 ll head[amn],etot; 17 struct eg{ 18 ll to,v; 19 db w; 20 eg(){} 21 eg(ll to,ll v,db w):to(to),v(v),w(w){} 22 }e[amn]; 23 void einit(){ 24 etot=0; 25 mem(head,0); 26 } 27 void add(ll u,ll v,db w){ 28 e[++etot]=eg(head[u],v,w); 29 head[u]=etot; 30 } 31 void sovle(); 32 int main(){ 33 ios::sync_with_stdio(0); 34 ll T=1; 35 //cin>>T; 36 while(T--){ 37 sovle(); 38 } 39 } 40 ll n,m,k; 41 ll s,t; 42 struct Node{ 43 int id; db d; 44 Node() {} 45 Node(int id, db d):id(id),d(d){} 46 bool operator < (const Node &A) const { 47 return d > A.d; 48 } 49 }; 50 ll vis[amn]; 51 db dis[amn]; 52 void dijkstra(int st){ 53 for(int i=1; i<=n; i++){ 54 vis[i] = 0; 55 dis[i] = inf; 56 } 57 58 dis[st] = 0; 59 priority_queue <Node> Q; 60 while(Q.size())Q.pop(); 61 Q.push(Node(st, 0)); 62 Node nd; 63 64 while(!Q.empty()){ 65 nd = Q.top(); Q.pop(); 66 if(vis[nd.id]) continue; 67 vis[nd.id] = true; 68 go(i,nd.id){ 69 int j = e[i].v; 70 db k = e[i].w; 71 if(nd.d + k < dis[j] && !vis[j]){ 72 dis[j] = nd.d + k; 73 Q.push(Node(j, dis[j])); 74 } 75 } 76 } 77 } 78 ll u[amn],v[amn]; 79 db x[amn],y[amn]; 80 void sovle(){ 81 cin>>n>>m>>s>>t; 82 rep(i,1,m){ 83 cin>>u[i]>>v[i]>>x[i]>>y[i]; 84 } 85 db ans=0,bs=1e-4; 86 for(db a=bs;a<=1;a+=bs){ 87 einit(); 88 rep(i,1,m){ 89 db w=x[i]+a*y[i]; 90 add(u[i],v[i],w); 91 add(v[i],u[i],w); 92 } 93 dijkstra(s); 94 ans+=dis[t]; 95 } 96 cout<<ans/(1e4)<<endl; 97 } 98 /* 99 100 */