poj1655 Balancing Act 求树的重心

直接dfs就可以了，记忆化都不需要。。复杂度o(N)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<vector>
#define REP(i,a,b) for(int i=a;i<=b;i++)
#define MS0(a) memset(a,0,sizeof(a))

using namespace std;

typedef long long ll;
const int maxn=1000100;
const int INF=1e9+10;

int n;
vector<int> G[maxn];
int u,v;
int point,balance;

int dfs(int u,int f)
{
    int cnt=1,balance1=0;
    for(int i=0;i<G[u].size();i++){
        int v=G[u][i];
        if(v==f) continue;
        int tmp=dfs(v,u);
        cnt+=tmp;
        balance1=max(balance1,tmp);
    }
    balance1=max(balance1,n-cnt);
    if(balance1<balance){
        balance=balance1;
        point=u;
    }
    return cnt;
}

int main()
{
    freopen("in.txt","r",stdin);
    int T;cin>>T;
    while(T--){
        scanf("%d",&n);
        REP(i,1,n) G[i].clear();
        REP(i,1,n-1){
            scanf("%d%d",&u,&v);
            G[u].push_back(v);
            G[v].push_back(u);
        }
        point=1,balance=INF;
        dfs(1,0);
        printf("%d %d
",point,balance);
    }
    return 0;
}