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 ",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 }