UVa 1292 - Strategic game

有两种做法：一种是经典二分图最小顶点覆盖，一种是树形DP，我用的后者。

 

第一次学习树形DP……

 

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <cstdlib>

 4 #include <vector>

 5 #include <algorithm>

 6 

 7 using namespace std;

 8 

 9 const int MAXN = 1600;

10 

11 int N, root;

12 int dp[MAXN][2];

13 vector<int> tree[MAXN];

14 

15 void init()

16 {

17     root = -1;

18 

19     for ( int i = 0; i < N; ++i )

20     {

21         int u, cnt;

22         tree[i].clear();

23         scanf("%d:(%d)", &u, &cnt );

24         if ( root == -1 ) root = u;

25         for ( int j = 0; j < cnt; ++j )

26         {

27             int v;

28             scanf( "%d", &v );

29             tree[u].push_back(v);

30         }

31     }

32     return;

33 }

34 

35 int DFS( int fa )

36 {

37     dp[fa][0] = 0;

38     dp[fa][1] = 1;

39     int len = tree[fa].size();

40     for ( int i = 0; i < len; ++i )

41     {

42         int v = tree[fa][i];

43         DFS( v );

44         dp[fa][0] += dp[v][1];

45         dp[fa][1] += min( dp[v][0], dp[v][1] );

46     }

47     return min( dp[fa][0], dp[fa][1] );

48 }

49 

50 int main()

51 {

52     while ( scanf( "%d", &N ) == 1 )

53     {

54         init();

55         printf( "%d\n", DFS(root) );

56     }

57     return 0;

58 }