POJ 2378 Tree Cutting

#include <iostream>
#include <cstdio>
#include <cstring>
#define REP(i, s, n) for(int i = s; i <= n; i ++)
#define REP_(i, s, n) for(int i = n; i >= s; i --)
#define MAX_N 10000 + 10

using namespace std;

int n, u, v;
struct node1{int v, next;} E[MAX_N << 1];
struct node2{int sum, cnt;} N[MAX_N];
int head[MAX_N], top = 0;

void add(int u, int v){
    E[++ top].v = v; E[top].next = head[u]; head[u] = top;
}

int Gao(int x, int last){
    N[x].sum = 1; N[x].cnt = 0;
    for(int i = head[x]; i; i = E[i].next){
        if(E[i].v != last){
            int t = Gao(E[i].v, x);
            N[x].sum += t; N[x].cnt = max(N[x].cnt, t);
        }
    }
    return N[x].sum;
}
 
int main(){
    scanf("%d", &n);
    REP(i, 1, n - 1){
        scanf("%d%d", &u, &v);
        add(u, v); add(v, u);
    }
    Gao(1, 0);
    int res = 99999999;
    REP(i, 1, n){
        N[i].cnt = max(N[i].cnt, n - N[i].sum);
        if(res > N[i].cnt) res = N[i].cnt;
    }
    
    if(res <= n / 2){
        REP(i, 1, n) if(N[i].cnt == res) printf("%d\n", i);
    }
    else printf("NONE\n");
    return 0;
}