【luogu P2590 [ZJOI2008]树的统计】 题解

题目链接：https://www.luogu.org/problemnew/show/P2590
我想学树剖QAQ

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 31000;
int fa[maxn], dep[maxn], size[maxn], son[maxn], top[maxn], seg[maxn], rev[maxn<<2];
int sum[maxn<<2], num[maxn], mx[maxn];
struct edge{
    int to, next;
}e[maxn<<2];
int head[maxn<<2], cnt;
int summ, maxx, n, m;
void query(int k, int l, int r, int L, int R)//区间查询
{
    if(L > r||R < l) return;
    if(L <= l&&r <= R)
    {
        summ += sum[k];
        maxx = max(maxx, mx[k]);
        return;
    }
    int mid = l+r>>1, res = 0;
    if(mid >= L) query(k<<1, l, mid, L, R);
    if(mid+1 <= R) query((k<<1)+1, mid+1, r, L, R);
}
void change(int k, int l, int r, int val, int pos)//单点修改 
{
    if(pos>r || pos<l) return;
    if(l == r && r == pos)
    {
        sum[k] = val;
        mx[k] = val;
        return;
    }
    int mid = l+r>>1;
    if(mid >= pos) change(k<<1, l, mid, val, pos);
    if(mid+1 <= pos) change((k<<1)+1, mid+1, r, val, pos);
    sum[k] = sum[k<<1]+sum[(k<<1)+1];
    mx[k] = max(mx[k<<1], mx[(k<<1)+1]);
}
void dfs1(int u, int f)
{
    int v;
    size[u] = 1;
    fa[u] = f;
    dep[u] = dep[f]+1;
    for(int i = head[u]; v = e[i].to, i; i = e[i].next)
    {
        if(v != f)
        {
            dfs1(v,u);
            size[u] += size[v];
            if(size[v] > size[son[u]])
            son[u] = v;
        }
    }
}
void dfs2(int u, int f)
{
    int v;
    if(son[u])
    {
        seg[son[u]] = ++seg[0];
        top[son[u]] = top[u];
        rev[seg[0]] = son[u];
        dfs2(son[u],u);
    }
    for(int i = head[u]; v = e[i].to, i; i = e[i].next)
    {
        if(!top[v])
        {
            seg[v] = ++seg[0];
            rev[seg[0]] = v;
            top[v] = v;
            dfs2(v,u);
        }
    }
}
void build(int k, int l, int r)
{
    int mid = l+r>>1;
    if(l == r)
    {
        mx[k] = sum[k] = num[rev[l]];
        return;
    }
    build(k<<1, l, mid);
    build((k<<1)+1, mid+1, r);
    sum[k] = sum[k<<1]+sum[(k<<1)+1];
    mx[k] = max(mx[k<<1],mx[(k<<1)+1]);
}
inline int read()
{
    char c;
    int k = 1;
    while((c = getchar())<'0' || c>'9')
        if(c == '-') k = -1;
    int res = c-'0';
    while((c = getchar())>='0' && c<='9')
        res = res*10+c-'0';
    return res*k;
}
inline void add(int u, int v)
{
    e[++cnt].next = head[u];
    e[cnt].to = v;
    head[u] = cnt;
}
inline void insert(int u, int v)
{
    add(u, v);
    add(v, u); 
}
inline void ask(int u, int v)
{
    int fu = top[u], fv = top[v];
    while(fu != fv)
    {
        if(dep[fu]<dep[fv]) swap(u,v), swap(fu,fv);
        query(1,1,seg[0],seg[fu],seg[u]);
        u = fa[fu], fu = top[u];
    }
    if(dep[u]>dep[v]) swap(u,v);
    query(1,1,seg[0],seg[u],seg[v]);
}
int main()
{
    n = read();
    for(int i = 1; i < n; i++)
    insert(read(),read());
    for(int i = 1; i <= n; i++)
    num[i] = read();
    dfs1(1,0);
    seg[0] = seg[1] = rev[1] = top[1] = 1;
    dfs2(1,0);
    build(1,1,seg[0]);
    m = read();
    char opt[10];
    int u, v;
    for(int i = 1; i <= m; i++)
    {
        scanf("%s",opt+1);
        u = read(); v = read();
        if(opt[1] == 'C')
            change(1,1,seg[0],v,seg[u]);
        else
        {
            summ = 0;
            maxx = -0x7fffffff;
            ask(u,v);
            if(opt[2] == 'M')
            printf("%d\n",maxx);
            else
            printf("%d\n",summ);    
        }       
    }
    return 0;
}