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aoj1162dist.cpp
76 lines (68 loc) · 1.55 KB
/
aoj1162dist.cpp
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#include <iostream>
#include <vector>
#include <string>
#include <cstdio>
#include <queue>
using namespace std;
#define N 30
#define INF 100000
struct road{int to,cost,lim;};
struct situ{int v,now,from;double d;};
bool operator < (const situ &a,const situ &b){
return a.d > b.d;
}
int main(){
while(1){
int n,m,s,g;
vector<road> roads[N];
cin >> n >> m;
if(!n&&!m) break;
cin >> s >> g;
s--;g--;
for(int i=0;i<m;i++){
int x,y,d,c;
scanf("%d%d%d%d",&x,&y,&d,&c);
x--;y--;
roads[x].push_back((road){y,d,c});
roads[y].push_back((road){x,d,c});
}
priority_queue<situ> que;
for(int i=0;i<roads[s].size();i++){
int to = roads[s][i].to;
int d = roads[s][i].cost;
que.push((situ){1,to,s,(double)d});
}
double dist[N][N][31];
for(int i=0;i<n;i++){
for(int j=0;j<n;j++){
for(int k=1;k<31;k++){
dist[i][j][k] = INF;
}
}
}
bool isClear = false;
while(que.size()){
situ st = que.top(); que.pop();
if(dist[st.now][st.from][st.v]<st.d) continue;
dist[st.now][st.from][st.v] = st.d;
if(st.now==g&&st.v==1){
printf("%.5f\n",st.d);
isClear = true;
break;
}
for(int i=0;i<roads[st.now].size();i++){
int to = roads[st.now][i].to;
int d = roads[st.now][i].cost;
if(to == st.from) continue;
for(int j=-1;j<=1;j++){
if(st.v+j<=roads[st.now][i].lim&&st.v+j>0){
//if(dist[to][st.now][st.v+j]>st.d+(double)d/(st.v+j))
que.push((situ){st.v+j,to,st.now,st.d+(double)d/(st.v+j)});
}
}
}
}
if(!isClear) cout << "unreachable" << endl;
}
return 0;
}