poj----1330Nearest Common Ancestors（简单LCA)

题目连接  http://poj.org/problem?id=1330

就是构建一棵树，然后问你两个节点之间最近的公共父节点是谁？

代码：

 1 /*Source Code

 2 Problem: 1330        User: huifeidmeng

 3 Memory: 1232K        Time: 63MS

 4 Language: C++        Result: Accepted

 5 

 6     Source Code

 7 */

 8     #include<iostream>

 9     #include<vector>

10     #include<cstdio>

11     #include<cstring>

12     #include<cstdlib>

13     using namespace std;

14     const int maxn=10002;

15     vector<int> tree[maxn],qus[maxn];

16     int rank[maxn],father[maxn];

17     bool vis[maxn];

18     int rudu[maxn];

19     int lroot[maxn];

20     void init(int n){

21          memset(vis,0,sizeof(vis));

22          memset(rudu,0,sizeof(rudu));

23          memset(lroot,0,sizeof(lroot));

24         for(int i=1;i<=n;i++){

25             father[i]=i;

26             rank[i]=1;

27             tree[i].clear();

28             qus[i].clear();

29         }

30     }

31     int find(int a){

32        while(a!=father[a])

33              a=father[a];

34         return a;

35     }

36     void Union(int a,int b)

37     {

38         int x=find(a);

39         int y=find(b);

40         if(x==y) return ;

41         if(rank[x]<rank[y]){

42           rank[y]+=rank[x];

43           father[x]=y;

44         }

45         else {

46          rank[x]+=rank[y];

47          father[y]=x;

48         }

49     }

50     void LCA(int u)

51     {

52       lroot[u]=u;

53       int len=tree[u].size();

54       for(int i=0;i<len;i++){

55           LCA(tree[u][i]);

56           Union(u,tree[u][i]);

57           lroot[find(u)]=u;

58       }

59       vis[u]=1;

60       int ss=qus[u].size();

61       for(int i=0;i<ss;i++){

62             if(vis[qus[u][i]]){

63                 printf("%d\n",lroot[find(qus[u][i])]);

64                 return ;

65             }

66       }

67     }

68     int main()

69     {

70       int cas,n,u1,u2;

71       //freopen("test.in","r",stdin);

72       scanf("%d",&cas);

73       while(cas--){

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

75           init(n);

76           for(int i=1;i<n;i++){

77           scanf("%d%d",&u1,&u2);

78           tree[u1].push_back(u2);

79           rudu[u2]++;  

80           }

81           scanf("%d%d",&u1,&u2);

82           qus[u1].push_back(u2);

83           qus[u2].push_back(u1);

84           for(int i=1;i<=n;i++){

85          if(0==rudu[i]){ //找到root

86            LCA(i);

87            break;

88           }

89           }

90       }

91     return 0;

92     }