POJ 1330 Nearest Common Ancestors LCA

/********************* Template ************************/
#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cassert>
#include <cstring>
#include <sstream>
#include <fstream>
#include <numeric>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <functional>
using namespace std;
#define EPS             1e-8
#define DINF            1e15
#define MAXN            10050
#define MOD             1000000007
#define INF             0x7fffffff
#define LINF            1LL<<60
#define PI              3.14159265358979323846
#define lson            l,m,rt<<1
#define rson            m+1,r,rt<<1|1
#define BUG             cout<<"BUG! "<<endl
#define ABS(a)          ((a)>0?(a):(-a))
#define LINE            cout<<"------------------ "<<endl
#define FIN             freopen("in.txt","r",stdin)
#define FOUT            freopen("out.txt","w",stdout)
#define mem(a,b)        memset(a,b,sizeof(a))
#define FOR(i,a,b)      for(int i = a ; i < b ; i++)
#define read(a)         scanf("%d",&a)
#define read2(a,b)      scanf("%d%d",&a,&b)
#define read3(a,b,c)    scanf("%d%d%d",&a,&b,&c)
#define write(a)        printf("%d
",a)
#define write2(a,b)     printf("%d %d
",a,b)
#define write3(a,b,c)   printf("%d %d %d
",a,b,c)
#pragma comment         (linker,"/STACK:102400000,102400000")
template<class T> inline T L(T a)               {return (a << 1);}
template<class T> inline T R(T a)               {return (a << 1 | 1);}
template<class T> inline T lowbit(T a)          {return (a & -a);}
template<class T> inline T Mid(T a,T b)         {return ((a + b) >> 1);}
template<class T> inline T gcd(T a,T b)         {return b ? gcd(b,a%b) : a;}
template<class T> inline T lcm(T a,T b)         {return a / gcd(a,b) * b;}
template<class T> inline T Min(T a,T b)         {return a < b ? a : b;}
template<class T> inline T Max(T a,T b)         {return a > b ? a : b;}
template<class T> inline T Min(T a,T b,T c)     {return min(min(a,b),c);}
template<class T> inline T Max(T a,T b,T c)     {return max(max(a,b),c);}
template<class T> inline T Min(T a,T b,T c,T d) {return min(min(a,b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d) {return max(max(a,b),max(c,d));}
template<class T> inline T mod(T x,T y)         {y = ABS(y); return x >= 0 ? x % y : x % y + y;}
template<class T> inline T mul_mod(T a,T b,T n) {
    T ret = 0,tmp = a % n;
    while(b){
        if((b&1) && (ret+=tmp)>=n) ret -= n;
        if((b>>=1) && (tmp<<=1)>=n) tmp -= n;
    }return ret;
}
template<class T> inline T pow_mod(T a,T b,T n){
    T ret = 1; a = a % n;
    while(b){
        if (b&1) ret = mul_mod(ret,a,n);
        if (b>>=1) a = mul_mod(a,a,n);
    }return ret;
}
template<class T> inline T exGCD(T a, T b, T &x, T &y){
    if(!b) return x = 1,y = 0,a;
    T res = exGCD(b,a%b,x,y),tmp = x;
    x = y,y = tmp - (a / b) * y;
    return res;
}
template<class T> inline T reverse_bits(T x){
    x = (x >> 1 & 0x55555555) | ((x << 1) & 0xaaaaaaaa); x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
    x = (x >> 4 & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0); x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
    x = (x >>16 & 0x0000ffff) | ((x <<16) & 0xffff0000); return x;
}
typedef long long LL;    typedef unsigned long long ULL;
//typedef __int64 LL;      typedef unsigned __int64 ULL;
/*********************   By  F   *********************/
vector<int> G[MAXN];
int fa[MAXN];
int lev[MAXN];
int root;
int n,u,v,T;
void init(){
    for(int i = 0 ; i < MAXN; i++) G[i].clear();
    mem(fa,0);
    mem(lev,0);
}
void dfs(int u,int dep){
    lev[u] = dep;
    for(int i = 0 ; i < G[u].size() ; i++){
        dfs(G[u][i],dep+1);
    }
}
int lca(int a,int b){
    while(lev[a] > lev[b]) a = fa[a];
    while(lev[a] < lev[b]) b = fa[b];
    while(a != b){
        a = fa[a];
        b = fa[b];
    }
    return a;
}
int main(){
    //FIN;
    //FOUT;
    scanf("%d",&T);
    while(T--){
        scanf("%d",&n);
        init();
        for(int i = 0 ; i < n-1 ; i++){
            scanf("%d%d",&u,&v);
            G[u].push_back(v);
            fa[v] = u;
        }
        scanf("%d%d",&u,&v);
        root = u;
        while(fa[root] != 0) root = fa[root];
        dfs(root,1);
        printf("%d
",lca(u,v));
    }
    return 0;
}

水题,没什么可说的