[poj1860] Currency Exchange (bellman-ford算法)

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <vector>
 5 #include <map>
 6 #include <set>
 7 #include <bitset>
 8 #include <cmath>
 9 #include <numeric>
10 #include <iterator>
11 #include <iostream>
12 #include <cstdlib>
13 using namespace std;
14 #define PB push_back
15 #define MP make_pair
16 #define SZ size()
17 #define ST begin()
18 #define ED end()
19 #define CLR clear()
20 #define ZERO(x) memset((x),0,sizeof(x))
21 typedef long long LL;
22 typedef unsigned long long ULL;
23 typedef pair<int,int> PII;
24 const double EPS = 1e-8;
25 
26 struct EDGE{
27     int from,to;
28     double r,c;
29     EDGE(int _from = 0, int _to =0 , double _r = 0, double _c = 0 ) :
30         from(_from),to(_to),r(_r),c(_c) {}
31 };
32 
33 vector<EDGE> vec;
34 int N,M,S;
35 double V;
36 double d[111];
37 
38 bool floyd(int s){
39     d[s] = V;
40     bool flag = false;
41     while(true){
42         flag = false;
43         for(int i=0;i<vec.SZ;i++){
44             const EDGE& e = vec[i];
45             if(d[e.from]>0.0 && d[e.to]<(d[e.from]-e.c)*e.r){
46                 d[e.to]=(d[e.from]-e.c)*e.r;
47                 flag = true;
48             }
49         }
50         if(d[s]>V) return true;
51         if(!flag) {
52             break;
53         }
54     }
55     return d[s]>V;
56 }
57 
58 
59 int main(){
60     while(EOF!=scanf("%d%d%d%lf",&N,&M,&S,&V)){
61         vec.CLR;
62         ZERO(d);
63         int from,to;
64         double rab,cab,rba,cba;
65         for(int i=0;i<M;i++){
66             scanf("%d%d%lf%lf%lf%lf",&from,&to,&rab,&cab,&rba,&cba);
67             vec.PB(EDGE(from,to,rab,cab));
68             vec.PB(EDGE(to,from,rba,cba));
69         }
70         puts(floyd(S)?"YES":"NO");
71     }
72     return 0;
73 }