hdu 1520 树形dp入门

和poj 1463基本一样。

 1 #include <algorithm>

 2 #include <iostream>

 3 #include <cstring>

 4 #include <cstdio>

 5 using namespace std;

 6 

 7 const int N = 6001;

 8 int head[N];

 9 int rating[N];

10 bool flag[N];

11 int dp[N][2];

12 int e, n;

13 

14 void init()

15 {

16     e = 0;

17     memset( flag, true, sizeof(flag) );

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

19 }

20 

21 struct Edge

22 {

23     int v, next;

24 } edge[N];

25 

26 void addEdge( int u, int v )

27 {

28     edge[e].v = v;

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

30     head[u] = e++;

31 }

32 

33 void dfs( int u )

34 {

35     dp[u][0] = 0;

36     dp[u][1] = rating[u];

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

38     {

39         int v = edge[i].v;

40         dfs(v);

41         dp[u][0] += max( dp[v][0], dp[v][1] );

42         dp[u][1] += dp[v][0];

43     }

44 }

45 

46 int main ()

47 {

48     while ( scanf("%d", &n) != EOF )

49     {

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

51         {

52             scanf("%d", rating + i);

53         }

54         init();

55         int v, u;

56         while ( scanf("%d%d", &v, &u) != EOF )

57         {

58             if ( v == 0 && u == 0 ) break;

59             addEdge( u, v );

60             flag[v] = false;

61         }

62         int root;

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

64         {

65             if ( flag[i] )

66             {

67                 root = i;

68                 break;

69             }

70         }

71         dfs(root);

72         int ans = max( dp[root][0], dp[root][1] );

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

74     }

75     return 0;

76 }