学步园

题意:

树杈上长苹果,统计苹果数.

思路:

将树通过dfs映射到线性序列, 用树状数组计数.

#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
const int MAXN = 100010;
int n,m;
int head[MAXN],num;
struct pool
{
    int v,next;
}g[MAXN];
void add(int u, int v)
{
    g[++num].v = v;
    g[num].next = head[u];
    head[u] = num;
}
inline int lowbit(int x)
{
    return x&(-x);
}
int l[MAXN],r[MAXN];
void dfs(int u)
{
    l[u] = ++num;
    for(int i=head[u];i;i=g[i].next)
    {
        //printf("i = %d, dfs(%d);\n",i,g[i].v);
        dfs(g[i].v);
    }
    r[u] = num;
}
int a[MAXN],c[MAXN];
int sum(int x)
{
    int ans = 0;
    for(;x>0;x^=lowbit(x))  ans += c[x];
    return ans;
}
void modify(int x, int d)
{
    for(;x<=n;x+=lowbit(x)) c[x] += d;
}
int main()
{
    scanf("%d",&n);
    for(int i=0,v,u;i<n-1;i++)
    {
        scanf("%d%d",&u,&v);
        add(u, v);
    }
    num = 0;
   // printf("&&&");
    dfs(1);
   // printf("***");
    for(int i=1;i<=n;i++)//init
    {
        a[i] = 1;
        c[i] = lowbit(i);
    }
    scanf("%d",&m);
    char s[5];
    while(m--)
    {
        scanf("%s%d",s,&num);
        if(s[0]=='C')
        {
            modify(l[num],a[num]?-1:1);
            a[num] ^= 1;
        }
        else
            printf("%d\n",sum(r[num])-sum(l[num]-1));
    }
}