hdu 3335 最大独立集，疑惑

有整除关系就建边，然后求最大独立集，不过还是不懂为什么建双向边hunagry返回结果除以2就会WA。

单向建边的AC代码：

 1 #include <iostream>

 2 #include <cstring>

 3 #include <cstdio>

 4 using namespace std;

 5 

 6 const int N = 1001;

 7 const int M = 1000000;

 8 bool visit[N];

 9 __int64 a[N];

10 int head[N];

11 int mark[N];

12 int n, e;

13 

14 struct Edge

15 {

16     int v, next;

17 } edge[M];

18 

19 void addEdge( int u, int v )

20 {

21     edge[e].v = v;

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

23     head[u] = e++;

24 }

25 

26 int dfs( int u )

27 {

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

29     {

30         int v = edge[i].v;

31         if ( !visit[v] )

32         {

33             visit[v] = true;

34             if ( mark[v] == -1 || dfs( mark[v] ) )

35             {

36                 mark[v] = u;

37                 return 1;

38             }

39         }

40     }

41     return 0;

42 }

43 

44 int hunagry()

45 {

46     memset( mark, -1, sizeof(mark) );

47     int res = 0;

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

49     {

50         memset( visit, 0, sizeof(visit) );

51         res += dfs(i);

52     }

53     return res;

54 }

55 

56 int main()

57 {

58     int t;

59     scanf("%d", &t);

60     while ( t-- )

61     {

62         e = 0;

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

64         scanf("%d", &n);

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

66         {

67             scanf("%I64d", a + i);

68             for ( int j = i - 1; j > 0; j-- )

69             {

70                 if ( a[i] % a[j] == 0 || a[j] % a[i] == 0 )

71                 {

72                     addEdge( j, i );

73                 }

74             }

75         }

76         int ans = n - hunagry();

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

78     }

79     return 0;

80 }