POJ 3321 Apple Tree

    树状数组。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
using namespace std;
#define N 100010

int vis[N],have[N];
int low[N],high[N];
int c[N];
vector< vector<int> > edge(N);
int n,now;

int lowbit(int x)
{
    return x&(-x);
}

void init()
{
    int i;
    for(i=1;i<N;i++)
    {
        have[i] = 1;
        c[i] = lowbit(i);
    }
    memset(vis,0,sizeof(vis));
    now = 1;
    return;
}

void modify(int x)
{
    int val;
    if(have[x])
    {
        have[x] = 0;
        val = -1;
    }
    else
    {
        have[x] = 1;
        val = 1;
    }
    while(x<=n)
    {
        c[x] += val;
        x += lowbit(x);
    }
}

void dfs(int v)
{
    vis[v] = 1;
    low[v] = now;
    for(int i=0;i<edge[v].size();i++)
    {
        if(!vis[edge[v][i]])
        {
            dfs(edge[v][i]);
        }
    }
    high[v] = now;
    now++;
}

int sum(int x)
{
    int res = 0;
    while(x>0)
    {
        res += c[x];
        x -= lowbit(x);
    }
    return res;
}

int main()
{
    int i,a,b,q,v;
    char ss[5];
    init();
    scanf("%d",&n);
    for(i=1;i<=n-1;i++)
    {
        scanf("%d%d",&a,&b);
        edge[a].push_back(b);
        edge[b].push_back(a);
    }
    dfs(1);
    scanf("%d",&q);
    while(q--)
    {
        scanf("%s",ss);
        if(ss[0] == 'Q')
        {
            scanf("%d",&v);
            printf("%d
",sum(high[v])-sum(low[v]-1));
        }
        else
        {
            scanf("%d",&v);
            modify(high[v]);
        }
    }
    return 0;
}