hdu 4607 Park Visit

求出树的直径d。当k<=d的时候，显然直接在直径上走就行了，当k>d的时候，便是直径d的长度 加上 多出来的点数*2.

#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
#include<cstring>
#define FF(i, a ,b) for(int i=a; i<b; i++)
#define FD(i, a ,b) for(int i=a; i>b; i--)
#define REP(i, n) for(int i=0; i<n; i++)
#define LL long long
#define CLR(a, b) memset(a, b, sizeof(a))
#define PB push_back
using namespace std;

const int maxn = 111111;
int n, m, dist, k, end;
vector<int> G[maxn];

void dfs(int x, int fa, int d)
{
    int nc = G[x].size();
    if(nc == 1)
    {
        if(d > dist)
        {
            dist = d;
            end = x;
        }
    }
    REP(i, nc)
    {
        int v = G[x][i];
        if(v != fa)
        {
            dfs(v, x, d+1);
        }
    }
}

int main()
{
    int T, a, b;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d%d", &n, &m);
        REP(i, n+1) G[i].clear();
        FF(i, 1, n)
        {
            scanf("%d%d", &a, &b);
            G[a].PB(b);
            G[b].PB(a);
        }
        dist = 0;
        dfs(1, -1, 0);
        dfs(end, -1, 0);
        dist++;
        while(m--)
        {
            scanf("%d", &k);
            if(k <= dist) printf("%d\n", k-1);
            else printf("%d\n", dist - 1 + (k-dist)*2);
        }
    }
    return 0;
}