POJ 1330 Nearest Common Ancestors（Tree）

#include<iostream>
#include<vector>
#include<cstdio>
#include<cstdlib>
#include<cstring>
using namespace std;

const int M = 10001;  
//vector<int> v[M];
int level[M];
int father[M];

void visitEveryone(vector<int> v[], int one, int _level)
{
    level[one] = _level;
    for(vector<int>::iterator it = v[one].begin(); it != v[one].end(); ++it)
    {
        visitEveryone(v, *it, _level+1);
    }
}

int main()
{
    int T,N,a,b,i,j;
    scanf("%d", &T);
    while(T--)
    {
        vector<int> v[M];
        scanf("%d", &N);
        memset(father, 0, (N+1)*sizeof(int));
        for(i = 1; i < N; ++i)
        {
            scanf("%d %d", &a, &b);
            father[b] = a;
            v[a].push_back(b);
        }
        scanf("%d %d", &a, &b);
        for(j=1; father[j] > 0 && j <= N; ++j);

        visitEveryone(v, j, 0);        
        
        while(a != b)
        {
     
            if(level[a] < level[b])
                b = father[b];
            else
                a = father[a];
        }         
 
        printf("%d\n",a);
    }
    return 0;
}