poj 3255(次短路)

求次短路。

 1 // File Name: 3255.cpp

 2 // Author: Missa

 3 // Created Time: 2013/4/5 星期五 1:01:09

 4 

 5 #include<iostream>

 6 #include<cstdio>

 7 #include<cstring>

 8 #include<algorithm>

 9 #include<cmath>

10 #include<queue>

11 #include<stack>

12 #include<string>

13 #include<vector>

14 #include<cstdlib>

15 #include<map>

16 #include<set>

17 using namespace std;

18 #define CL(x,v) memset(x,v,sizeof(x));

19 #define R(i,st,en) for(int i=st;i<en;++i)

20 #define LL long long

21 #define inf 0x3f3f3f3f

22 

23 const int maxn = 5e3+5;

24 int n,m;

25 struct edge

26 {

27     int v, c;

28     edge(){}

29     edge(int v, int c):v(v), c(c){}

30 };

31 vector <edge> adj[maxn];

32 

33 int dij(int src)

34 {

35     bool vis[maxn][2];

36     CL(vis,0);

37     int dis[maxn][2];

38     int u,v,c;

39     CL(dis,0x3f);

40     dis[src][0] = 0;

41     for (int i = 0; i <= 2 * n; ++i)

42     {

43         int tmp = inf, u = src, p = 0;

44         for (int j = 1; j <= n; ++j)

45         {

46             if(!vis[j][0] && tmp > dis[j][0])

47             {

48                 tmp = dis[j][0];

49                 u = j;

50                 p = 0;

51             }

52             else if(!vis[j][1] && tmp > dis[j][1])

53             {

54                 tmp = dis[j][1];

55                 u = j;

56                 p = 1;

57             }

58         }

59         if(tmp == inf) break;

60         vis[u][p] = 1;

61         for (int j = 0; j < adj[u].size(); ++j)

62         {

63             v = adj[u][j].v;

64             c = adj[u][j].c;

65             if (dis[v][0] > tmp + c)

66             {

67                 dis[v][1] = dis[v][0];

68                 dis[v][0] = tmp + c;

69             }

70             else if (dis[v][1] > tmp + c)

71             {

72                 dis[v][1] = tmp + c;

73             }

74         }

75     }

76     return dis[n][1];

77 }

78 

79 int main()

80 {

81     int u, v, c;

82     while(~scanf("%d%d", &n, &m))

83     {

84         CL(adj, 0);

85         while(m--)

86         {

87             scanf("%d%d%d",&u, &v, &c);

88             adj[u].push_back(edge(v,c));

89             adj[v].push_back(edge(u,c));

90         }

91         printf("%d\n",dij(1));

92     }

93     return 0;

94 }