1103 POI2007 大都市meg

    树链剖分水过，单点修改，树状数组即可。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define N 250100
using namespace std;

int n, m, nowplace = 0;
int p[N] = {0}, next[N], v[N], bnum = 0;
int son[N] = {0}, fa[N], w[N], top[N], deep[N] = {0}, num[N];
int t[N] = {0};

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

void dfs_1(int now, int fat)
{
    int k = p[now]; num[now] = 1; int maxson = 0;
    fa[now] = fat; deep[now] = deep[fat] + 1;
    while (k)
    {
        dfs_1(v[k], now);
        if (num[v[k]] > maxson)
        {
            maxson = num[v[k]];
            son[now] = v[k];
        }
        num[now] += num[v[k]];
        k = next[k];
    }
}

void dfs_2(int now, int nowtop)
{
    int k = p[now]; w[now] = ++nowplace; top[now] = nowtop;
    if (son[now]) dfs_2(son[now], nowtop);
    while (k)
    {
        if (v[k] != son[now])
            dfs_2(v[k], v[k]);
        k = next[k];
    }
}

void add(int now, int addnum)
{
    while (now <= n)
    {
        t[now] += addnum;
        now += lowbit(now);
    }
    return;
}

int task(int now)
{
    int ans = 0;
    while (now)
    {
        ans += t[now];
        now -= lowbit(now);
    }
    return ans;
}

int ask(int u, int v)
{
    int f1 = top[u], f2 = top[v];
    if (deep[f1] < deep[f2]) { swap(f1, f2); swap(u, v); }
    if (f1 == f2) return task(max(w[u], w[v])) - task(min(w[u], w[v])-1);
    else
    {
        int ans = 0;
        ans = task(w[u]) - task(w[f1]-1); // 搞清先后
        ans += ask(fa[f1], v);
        return ans;
    }
}

int main()
{
    scanf("%d", &n);
    for (int i = 1; i < n; ++i)
    {
        int x, y; scanf("%d%d", &x, &y);
        if (x > y) swap(x, y);
        bnum++; next[bnum] = p[x]; p[x] = bnum; v[bnum] = y;
    }
    dfs_1(1, 0); dfs_2(1, 1);
    for (int i = 2; i <= n; ++i) add(w[i], 1);
    scanf("%d", &m); m = m+n-1;
    for (int i = 1; i <= m; ++i)
    {
        char s[2]; scanf("%s", s);
        if (s[0] == 'A')
        {
            int x, y; scanf("%d%d", &x, &y);
            if (x > y) swap(x, y);
            add(w[y], -1);
        }
        else
        {
            int x; scanf("%d", &x);
            printf("%d
", ask(1, x));
        }
    }
    return 0;
}

还有DFS序做法，其实就是求点到根的路径权值和，样例的DFS序 为 1 4 5 5 4 3 3 2 2 1

我们把入序的地方+1 出序的地方-1， 查询的时候求入序的前缀和 - 1 就OK了（因为要减去多出来的1节点）

修改的时候入序和出序都改为0

上代码：

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define N 250010
using namespace std;

int n, m, nowplace = 0;
int p[N] = {0}, next[N], v[N], bnum = 0;
int t[N*2] = {0};
int first[N], second[N];

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

void add(int now, int addnum)
{
    while (now <= 2*n)
    {
        t[now] += addnum;
        now += lowbit(now);
    }
}

void dfs(int now)
{
    int k = p[now]; add(++nowplace, 1);
    first[now] = nowplace;
    while (k)
    {
        dfs(v[k]);
        k = next[k];
    }
    add(++nowplace, -1);
    second[now] = nowplace;
}

int ask(int now)
{
    int ans = 0;
    while (now)
    {
        ans += t[now];
        now -= lowbit(now);
    }
    return ans;
}

int main()
{
    scanf("%d", &n);
    for (int i = 1; i < n; ++i)
    {
        int x, y; scanf("%d%d", &x, &y);
        if (x > y) swap(x, y);
        bnum++; next[bnum] = p[x]; p[x] = bnum; v[bnum] = y;
    }
    dfs(1);
    scanf("%d", &m); m = m+n-1;
    for (int i = 1; i <= m; ++i)
    {
        char s[2]; scanf("%s", s);
        if (s[0] == 'A')
        {
            int x, y; scanf("%d%d", &x, &y);
            if (x < y) swap(x, y);
            add(first[x], -1);
            add(second[x], 1);
        }
        else
        {
            int x; scanf("%d", &x);
            printf("%d
", ask(first[x])-1);
        }
    }
    return 0;
}