POJ 3259 Wormholes(SPFA判负环)

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <queue>
 5 using namespace std;
 6 const int MAXN = 1e3 + 5;
 7 const int INF = 1e9;
 8 struct data {
 9     int next , to , cost;
10 }edge[MAXN * 10];
11 int head[MAXN] , d[MAXN] , cnt[MAXN] , cont;
12 bool vis[MAXN];
13 
14 void init(int n) {
15     for(int i = 1 ; i <= n ; i++) {
16         d[i] = INF;
17         cnt[i] = 0;
18         head[i] = -1;
19         vis[i] = false;
20     }
21     cont = 0;
22 }
23 
24 inline void add(int u , int v , int cost) {
25     edge[cont].next = head[u];
26     edge[cont].to = v;
27     edge[cont].cost = cost;
28     head[u] = cont++;
29 }
30 
31 bool spfa(int s , int n) {
32     d[s] = 0;
33     queue <int> que;
34     while(!que.empty()) {
35         que.pop();
36     }
37     que.push(s);
38     while(!que.empty()) {
39         int temp = que.front();
40         que.pop();
41         vis[temp] = false;
42         for(int i = head[temp] ; ~i ; i = edge[i].next) {
43             int v = edge[i].to;
44             if(d[v] > d[temp] + edge[i].cost) {
45                 d[v] = d[temp] + edge[i].cost;
46                 if(!vis[v]) {
47                     que.push(v);
48                     vis[v] = true;
49                     cnt[v]++;
50                     if(cnt[v] >= n)
51                         return true;
52                 }
53             }
54         }
55     }
56     return false;
57 }
58 
59 int main()
60 {
61     int n , m , c , u , v , cost , t;
62     scanf("%d" , &t);
63     while(t--) {
64         scanf("%d %d %d" , &n , &m , &c);
65         init(n);
66         while(m--) {
67             scanf("%d %d %d" , &u , &v , &cost);
68             add(u , v , cost);
69             add(v , u , cost);
70         }
71         while(c--) {
72             scanf("%d %d %d" , &u , &v , &cost);
73             add(u , v , -cost);
74         }
75         if(spfa(1 , n)) {
76             printf("YES\n");
77         }
78         else {
79             printf("NO\n");
80         }
81     }
82 }