POJ 1860（spfa）

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <queue>
 4 
 5 using namespace std;
 6 
 7 
 8 int m,n,p,head[ 10005 ],pos,num[ 10005 ];
 9 bool vis[ 10005 ];
10 double val,dist[ 10005 ];
11 
12 struct note{
13     int v,next;
14     double r,c;
15 }edge[ 10005 ];
16 
17 void add(int x,int v,double r,double c)
18 {
19     edge[ pos ].v = v;
20     edge[ pos ].r = r;
21     edge[ pos ].c = c;
22     edge[ pos ].next = head[ x ];
23     head[ x ] = pos ++;
24 }
25 
26 bool spfa()
27 {
28     queue<int >s;
29     s.push(p);
30     dist[ p ] = val;
31     vis[ p ] = true;
32     num[ p ] ++;
33     while(!s.empty())
34     {
35         int tmp = s.front();
36         s.pop();
37         vis[ tmp ] = false;
38         for( int i = head[ tmp ] ; i != -1 ; i = edge[ i ].next)
39         {
40             if( dist[ edge[ i ].v ] < (dist[ tmp ] - edge[ i ].c ) * edge[ i ].r )
41             {
42                 dist[ edge[ i ].v ] = (dist[ tmp ] - edge[ i ].c ) * edge[ i ].r;
43                 if( !vis[ edge[ i ].v ] )
44                 {
45                     s.push( edge[ i ].v );
46                     vis[ edge[ i ].v ] = true;
47                     num[ edge[ i ].v ] ++;     //可能构成正权回路，这个是用来判断的。但次数比m次要大的时候，就肯定是增多的。可以直接return 。
48                     if( num[edge[ i ].v] > m)
49                         return true;
50                 }
51             }
52         }
53     }
54     if( dist[ p ] > val ) return true;   //如果之后的钱比之前的多，也return true.
55     return false;
56 }
57 
58 int main()
59 {
60    // freopen("in.txt","r",stdin);
61     int a,b;
62     double r1,c1,r2,c2;
63     pos = 1;
64     memset( head , -1 , sizeof( head ) );
65     memset( dist , 0 , sizeof( dist ) );
66     memset( vis , false ,sizeof( vis ) );
67     memset( num , 0 , sizeof( num ) );
68     scanf("%d%d%d%lf",&m,&n,&p,&val);
69     for( int i = 1 ; i <= n ; i++ )
70     {
71         scanf("%d%d%lf%lf%lf%lf",&a,&b,&r1,&c1,&r2,&c2);
72         add(a,b,r1,c1);
73         add(b,a,r2,c2);
74     }
75     if(spfa()) printf("YES\n");
76     else printf("NO\n");
77     return 0;
78 }