pku1655 Balancing Act

http://poj.org/problem?id=1655

树状DP，双向建图，以1为树的根节点遍历一遍

#include <stdio.h>
#include <string.h>
#include <vector>

#define N 20010

using namespace std;

vector<int> a[N];

int n, mark[N], result, resulti;

int dfs(int x)
{
    int i, j, temp, sum = 1, max_son = 0;
    //printf("%d: ( ", x);
    for(i=0; i<a[x].size(); i++)
    {
        j = a[x][i];
        if(!mark[j])
        {
            mark[j] = 1;
            temp = dfs(j);
            sum += temp;
            max_son = max(max_son, temp);
        }
    }
    max_son = max(n-sum, max_son);
    if(max_son < result)
    {
        result = max_son;
        resulti = x;
    }
    //printf(" *%d %d) ", sum, max_son);
    return sum;
}

int main()
{
    int t, i, x, y;
    scanf("%d", &t);
    while(t-- && scanf("%d", &n))
    {
        for(i=1; i<=n; i++)
        {
            a[i].clear();
        }
        for(i=2; i<=n; i++)
        {
            scanf("%d%d", &x, &y);
            a[x].push_back(y);
            a[y].push_back(x);
        }
        memset(mark, 0, sizeof(mark));
        result = 1<<30;
        resulti = -1;
        mark[1] = 1;
        dfs(1);
        printf("%d %d\n", resulti, result);
    }
    return 0;
}