POJ 1655 Balancing Act 树形DP入门题

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;

const int maxn = 20003;

struct node
{
    int v, next, w;
}edge[maxn<<1];

int tot;
int head[maxn];
int n;

void init()
{
    tot = 0;
    memset(head, -1, sizeof(int) * (n+1));
}

void add(int x, int y)
{
    edge[tot].v = y;
    edge[tot].next = head[x];
    head[x] = tot++;
}

int maxz(int a, int b)
{
    return a > b ? a : b;
}

int minz(int a, int b)
{
    return a < b ? a : b;
}

int ans, kk;
int num[maxn];

void dfs(int u, int p)
{
    int i, tmp = 0;
    num[u] = 0;
    for(i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].v;
        if(v == p) continue;
        dfs(v, u);
        tmp = maxz(tmp, num[v] + 1);
        num[u] += num[v] + 1;
    }
    tmp = maxz(tmp, n - num[u] - 1);
    if(ans > tmp)
    {
        ans = tmp;
        kk = u;
    }
}

int main()
{
    int i, j, cas;
    int x, y;
    scanf("%d", &cas);
    while(cas--)
    {
        scanf("%d", &n);
        init();
        for(i = 1; i < n; i++)
        {
            scanf("%d%d", &x, &y);
            add(x, y);
            add(y, x);
        }
        ans = 1<<29;
        dfs(1, -1);
        printf("%d %d\n", kk, ans);
    }
    return 0;
}
/*
8
7
2 6
1 2
1 4
4 5
3 7
3 1
*/