hdu 1142 最短路+记忆化搜索

先求一遍最短路，然后判断哪条路可以走+记忆化搜索统计方法数。

 1 #include <algorithm>

 2 #include <iostream>

 3 #include <cstring>

 4 #include <cstdio>

 5 using namespace std;

 6 

 7 const int INF = 99999999;

 8 const int N = 1001;

 9 const int M = N * N;

10 int head[N];

11 int dist[N];

12 int dp[N];

13 bool visit[N];

14 int n, m, e;

15 

16 struct Edge

17 {

18     int v, next, w;

19 } edge[M];

20 

21 void addEdge( int u, int v, int w )

22 {

23     edge[e].v = v;

24     edge[e].w = w;

25     edge[e].next = head[u];

26     head[u] = e++;

27 }

28 

29 void dij( int s )

30 {

31     memset( visit, false, sizeof(visit) );

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

33     {

34         dist[i] = INF;

35     }

36     dist[s] = 0;

37     for ( int i = 1; i <= n; i++ )

38     {

39         int u = 0;

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

41         {

42             if ( !visit[j] && dist[j] < dist[u] )

43             {

44                 u = j;

45             }

46         }

47         visit[u] = true;

48         for ( int j = head[u]; j != -1; j = edge[j].next )

49         {

50             int v = edge[j].v, w = edge[j].w;

51             if ( !visit[v] && dist[u] + w < dist[v] )

52             {

53                 dist[v] = dist[u] + w;

54             }

55         }

56     }

57 }

58 

59 int dfs( int u )

60 {

61     if ( dp[u] ) return dp[u];

62     int sum = 0;

63     for ( int i = head[u]; i != -1; i = edge[i].next )

64     {

65         int v = edge[i].v;

66         if ( dist[u] > dist[v] )

67         {

68             sum += dfs(v);

69         }

70     }

71     return dp[u] = sum;

72 }

73 

74 int main ()

75 {

76     while ( scanf("%d", &n), n )

77     {

78         e = 0;

79         memset( head, -1, sizeof(head) );

80         scanf("%d", &m);

81         while ( m-- )

82         {

83             int u, v, w;

84             scanf("%d%d%d", &u, &v, &w);

85             addEdge( u, v, w );

86             addEdge( v, u, w );

87         }

88         dij(2);

89         memset( dp, 0, sizeof(dp) );

90         dp[2] = 1;

91         int ans = dfs(1);

92         printf("%d\n", ans);

93     }

94     return 0;

95 }