学步园

求树的直径

#include <stdio.h>   
#include <string.h>
const int MAXN = 100010;
struct node
{
	int to, next;
}data[MAXN*2];
int head[MAXN], n, m, sz;
void add(int u, int v)
{
	data[sz].to = v;
	data[sz].next = head[u];
	head[u] = sz++;
	data[sz].to = u;
	data[sz].next = head[v];
	head[v] = sz++;
}
int fnum[MAXN], snum[MAXN], cnt[MAXN];
void dfs(int u, int pre)
{
	int v, i;
	fnum[u] = snum[u] = 0;
	for (i = head[u]; ~i; i=data[i].next)
	{
		if ( (v=data[i].to) == pre) continue;
		dfs(v, u);
		if (fnum[v]+1 > fnum[u])
		{
			snum[u] = fnum[u];
			fnum[u] = fnum[v]+1;
		}
		else if (fnum[v]+1 > snum[u])
		{
			snum[u] = fnum[v]+1;
		}
	}
	i = head[u];
	if (u != 1)
	if (i == -1 || data[i].next == -1)	/// leaf node
	{
		fnum[u]=snum[u] = 0;
		cnt[u] = 0;
		return;
	}
	int c1=0, c2=0;
	for (i = head[u]; ~i; i=data[i].next)
	{
		if ( (v=data[i].to) == pre) continue;
		if (fnum[u] == fnum[v]+1) c1++;
		else if (snum[u] == fnum[v]+1) c2++;
	}
	if (c1 >= 2)
	{
		cnt[u] = fnum[u]*2;
	}
	else if (c1 >= 1 && c2 >= 1)
	{
		cnt[u] = fnum[u]+snum[u];
	}
	else
		cnt[u] = fnum[u];
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
#endif // ONLINE_JUDGE
	int t;
	scanf("%d", &t);
	while (t--)
	{
		scanf("%d%d", &n, &m);
		sz = 0;
		memset(head, -1, sizeof head);
		for (int i = 1; i< n; i++)
		{
			int u, v;
			scanf("%d%d", &u, &v);
			add(u, v);
		}
		dfs(1, -1);
		int mx = 0;
		for (int i = 1; i<= n; ++i)
		{
			if (cnt[i] > mx) mx=cnt[i];
		}
		++mx;
		for (int i = 0; i< m; ++i)
		{
			scanf("%d", &sz);
			if (sz <= mx)
				printf("%d\n", sz-1);
			else
				printf("%d\n", mx-1+(sz-mx)*2);
		}
	}
    return 0;
}