Luogu P3038 [USACO11DEC]牧草种植Grass Planting

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <complex>
#include <algorithm>
#include <climits>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <iomanip>
#define
#define

using namespace std;
typedef long long ll;
namespace Seg {
  struct node {
    int l, r, w, f;
  }tree[A];
  void build(int k, int l, int r) {
    tree[k].l = l; tree[k].r = r; tree[k].w = 0;
    if (l == r) return;
    int m = (l + r) >> 1;
    build(k << 1, l, m);
    build(k << 1 | 1, m + 1, r);
  }
  void down(int k) {
    tree[k << 1].f += tree[k].f;
    tree[k << 1 | 1].f += tree[k].f;
    tree[k << 1].w += (tree[k << 1].r - tree[k << 1].l + 1) * tree[k].f;
    tree[k << 1 | 1].w += (tree[k << 1 | 1].r - tree[k << 1 | 1].l + 1) * tree[k].f;
    tree[k].f = 0;
  }
  void change(int k, int l, int r) {
    if (tree[k].l >= l and tree[k].r <= r) {
      tree[k].w++; tree[k].f++;
      return;
    }
    if (tree[k].f) down(k);
    int m = (tree[k].l + tree[k].r) >> 1;
    if (l <= m) change(k << 1, l, r);
    if (r > m) change(k << 1 | 1, l, r);
    tree[k].w = tree[k << 1].w + tree[k << 1 | 1].w;
  }
  int ask(int k, int l, int r) {
    if (tree[k].l >= l and tree[k].r <= r) return tree[k].w;
    int m = (tree[k].l + tree[k].r) >> 1, ans = 0;
    if (tree[k].f) down(k);
    if (l <= m) ans += ask(k << 1, l, r);
    if (r > m) ans += ask(k << 1 | 1, l, r);
    return ans;
  }
};
int dfn[A], dep[A], fa[A], top[A], son[A], siz[A], cnt, pre[A];
namespace Cut {
  struct node {
    int next, to;
  }e[A];
  int head[A], num;
  void add(int fr, int to) {
    e[++num].next = head[fr];
    e[num].to = to;
    head[fr] = num;
  }
  void prepare(int fr) {
    siz[fr] = 1;
    for (int i = head[fr]; i; i = e[i].next) {
      int ca = e[i].to;
      if (ca == fa[fr]) continue;
      fa[ca] = fr;
      dep[ca] = dep[fr] + 1;
      prepare(ca);
      siz[fr] += siz[ca];
      if (siz[ca] > siz[son[fr]]) son[fr] = ca;
    }
  }
  void dfs(int fr, int tp) {
    dfn[fr] = ++cnt, pre[cnt] = fr, top[fr] = tp;
    if (!son[fr]) return;
    dfs(son[fr], tp);
    for (int i = head[fr]; i; i = e[i].next) {
      int ca = e[i].to;
      if (ca == fa[fr] or ca == son[fr]) continue;
      dfs(ca, ca);
    }
  }
  void change(int x, int y) {
    while (top[x] != top[y]) {
      if (dep[top[x]] < dep[top[y]]) swap(x, y);
      Seg::change(1, dfn[top[x]], dfn[x]);
      x = fa[top[x]];
    }
    if (dep[x] > dep[y]) swap(x, y);
    Seg::change(1, dfn[x] + 1, dfn[y]);
  }
  int ask(int x, int y, int ans = 0) {
    while (top[x] != top[y]) {
      if (dep[top[x]] < dep[top[y]]) swap(x, y);
      ans += Seg::ask(1, dfn[top[x]], dfn[x]);
      x = fa[top[x]];
    }
    if (dep[x] > dep[y]) swap(x, y);
    ans += Seg::ask(1, dfn[x] + 1, dfn[y]);
    return ans;
  }
}
int n, m, a, b;

int main(int argc, char const *argv[]) {
  cin >> n >> m;
  for (int i = 2; i <= n; i++) {
    cin >> a >> b;
    Cut::add(a, b); Cut::add(b, a);
  }
  Cut::prepare(1); Cut::dfs(1, 1); Seg::build(1, 1, n);
  while (m--) {
    char opt; cin >> opt >> a >> b;
    if (opt == 'P') Cut::change(a, b);
    else cout << Cut::ask(a, b) << endl;
  }
  return 0;
}