nyoj 天下第一 (spfa)

要求路径长度大于一，判断出环即可结束。。

 

 1 #include<iostream>

 2 #include<cstdio>

 3 #include<cstdlib>

 4 #include<cstring>

 5 #include<string>

 6 #include<queue>

 7 #include<algorithm>

 8 #include<map>

 9 #include<iomanip>

10 #include<climits>

11 #include<string.h>

12 #include<cmath>

13 #include<stdlib.h>

14 #include<vector>

15 #include<set>

16 #define INF 1e7

17 #define MAXN 100010

18 #define maxn 1000010

19 #define Mod 1000007

20 #define N 1010

21 using namespace std;

22 typedef long long LL;

23 

24 struct node{ int x; double w; };

25 vector<node> G[1010];

26 int u, v;

27 double w;

28 int n, m;

29 int T;

30 int cnt[555];

31 int vis[555];

32 double dis[555];

33 

34 bool  spfa()

35 {

36     queue<node> q;

37     q.push({ 1, 0 });

38     vis[1] = 1;

39     dis[1] = 1;

40     while (!q.empty()){

41         node now = q.front();

42         q.pop();

43         vis[now.x] = 0;

44         for (int i = 0; i < G[now.x].size(); ++i) {

45             node v = G[now.x][i];

46             if (dis[now.x] * v.w > dis[v.x]) {

47                 dis[v.x] = dis[now.x] * v.w;

48                 if (!vis[v.x]) {

49                     vis[v.x] = 1;

50                     cnt[v.x]++;

51                     q.push({ v.x, dis[v.x] });

52                     if (cnt[v.x] >= n) return true;

53                 }

54             }

55         }

56     }

57     return false;

58 }

59 

60 void init()

61 {

62     memset(dis,0,sizeof(dis));

63     memset(vis,0,sizeof(vis));

64     memset(cnt,0,sizeof(cnt));

65     for (int i = 0; i <= n; ++i)

66         G[i].clear();

67 }

68 

69 void run()

70 {

71     cin >> n >> m;

72     init();

73     for (int i = 0; i < m; ++i) {

74         cin >> u >> w >> v;

75         G[u].push_back({v,w});

76     }

77     if (spfa()) puts("Yes");

78     else puts("No");

79 }

80 

81 int main()

82 {

83     cin >> T;

84     while (T--)

85         run();

86     //system("pause");

87     return 0;

88 }