POJ 3321-Apple Tree-树状数组+dfs序

计算一个树的子树节点权值和，节点权值可以单个修改。

利用dfs序把一颗树投影到数组里，维护dfs序和子节点个数，然后用树状数组即可。

#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;

const int maxn = 1e5+10;
int N,M,c[maxn],chdnum[maxn];
int id_dfs[maxn],cnt_dfs;
bool vis[maxn];

struct Edge{
    int to,next;

}edge[4*maxn];
int head[maxn],tol;

int add_edge(int u,int v)
{
    edge[tol].to = u;
    edge[tol].next = head[v];
    head[v] = tol++;

    edge[tol].to = v;
    edge[tol].next = head[u];
    head[u] = tol++;
}

int dfs(int u)
{
    int chd = 1;
    vis[u] = true;
    if(id_dfs[u] == -1) id_dfs[u] = cnt_dfs++;

    for(int i = head[u];~i;i = edge[i].next) if(!vis[edge[i].to])
    {
        int v = edge[i].to;
        chd += dfs(v);
    }
    return chdnum[u] = chd;
}

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

void update(int x,int a)
{
    while( x <= N)
    {
        c[x] += a;
        x += lowbit(x);
    }
}

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

int query(int l,int r)
{
    return getsum(r) - getsum(l-1);
}

int main()
{
    while(~scanf("%d",&N))
    {
        memset(head,-1,sizeof head);
        memset(c,0,sizeof c);
        memset(id_dfs,-1,sizeof id_dfs);
        memset(vis,false,sizeof vis);
        cnt_dfs = 1;
        tol = 0;

        for(int i=0,u,v;i<N-1;i++)
        {
            scanf("%d%d",&u,&v);
            add_edge(u,v);
        }

        dfs(1);

        for(int i=1;i<=N;i++)
        {
            //printf("i: dfs:%d
",i,id_dfs[i]);
            update(id_dfs[i],1);
        }
        scanf("%d",&M);

        char op[5];
        int x;
        for(int i=0;i<M;i++)
        {
            scanf("%s%d",op,&x);
            //printf("sum:%d chnum:%d id:%d
",query(id_dfs[x],id_dfs[x]),chdnum[x],id_dfs[x]);
            if(op[0] == 'Q')
            {
                printf("%d
",getsum(id_dfs[x]+chdnum[x]-1) - getsum(id_dfs[x]-1) );
            }
            else
            {
                if(query(id_dfs[x],id_dfs[x])) update(id_dfs[x],-1);
                else         update(id_dfs[x],1);
            }
        }
    }
}