链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=20


邻接表+BFS


#include <iostream>
#include <vector>
#include <queue>
#define MAX_N 100000
using namespace std;
int M;
typedef pair<int ,int> P;       // 节点编号，距离
vector<P> G[MAX_N+5];
bool vis[MAX_N+5];				//访问标记
int pos[MAX_N+5];           //顺序
int N,S;
void init()
{
    for(int i=0;i<MAX_N+5;i++)
    {
        vis[i]=false;
        pos[i]=0;
        G[i].clear();

    }
    vis[S]=true;
}
void bfs()
{
    queue<P> que;
    que.push(make_pair(S,0));           //压入起点

    while(que.size())
    {
        P p=que.front();que.pop();
        int d=p.second,v=p.first;


        for(unsigned int i=0;i<G[v].size();i++)            //向连通的村庄扩散
        {
			int vt=G[v].at(i).first;
			if(vis[vt]==false)                 //无环图，防止重复
            {

                G[v].at(i).second=d+1;        //距离+1
				vis[vt]=true;				//已访问过
                que.push(G[v].at(i));
                pos[vt]=max(pos[vt],d+1);

            }


        }
    }

}
void solve()
{
    cin>>M;
    int a,b;
    while(M--)
    {

        cin>>N>>S;
        init();
        for(int i=0;i<N-1;i++)
        {
            cin>>a>>b;
            G[a].push_back(make_pair(b,0));     //无向图
            G[b].push_back(make_pair(a,0));

        }
        bfs();
        for(int i=1;i<=N;i++)
        {
            if(S==i)
            {
                cout<<"-1 ";
                continue;
            }
            for(unsigned int j=0;j<G[i].size();j++)
            {
                int vt=G[i].at(j).first;
                if(pos[vt]==pos[i]-1)
                    cout<<vt<<" ";
            }
        }
        cout<<endl;

    }

}

int main()
{
    solve();

    return 0;
}