樹鏈剖分模板題目。

樹鏈剖分，就是先選定好根節點，由根節點往下，沿著子樹節點最多的節點往下，將其拆成鏈，再由鏈組成線段樹的資料結構

#pragma comment(linker,"/STACK:100000000,100000000")
#include <iostream>
#include <stdio.h>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 50010;
struct Edge{
    int to, next;
};
int n, m, Q;
Edge edge[2*MAXN];
int head[MAXN], tot;
int top[MAXN];//每個節點所在鏈的頭節點的位置
int fa[MAXN];//每個節點的父親節點
int deep[MAXN];//每個節點的深度
int num[MAXN];//以第i個節點為根節點時子節點的個數
int p[MAXN];//i節點線上段樹的位置
int fp[MAXN];//p的反函式
int son[MAXN];//每個節點的最大分支的兒子節點
int a[MAXN];
int pos;
void init()
{
    tot = 0;
    memset(head, -1, sizeof(head));
    pos = 1;
    memset(son, -1, sizeof(son));
}
void addedge(int u, int v)
{
    edge[tot].to = v; edge[tot].next = head[u];
    head[u] = tot++;
}
void dfs1(int u, int father ,int dep)
{
    deep[u] = dep;
    fa[u] = father;
    num[u] = 1;
    for (int i = head[u]; ~i; i = edge[i].next) {
        int v = edge[i].to;
        if (v != father) {
            dfs1(v, u, dep+1);
            num[u] += num[v];
            if (son[u] == -1 || num[v] > num[son[u]])
                son[u] = v;
        }   
    }
}
void getpos(int u, int sp)
{
    top[u] = sp;
    p[u] = pos++;
    fp[p[u]] = u;
    if (son[u] == -1) return;
    getpos(son[u], sp);
    for (int i = head[u]; ~i; i = edge[i].next) {
        int v = edge[i].to;
        if (v != fa[u] && v != son[u]) {
            getpos(v, v);
        }
    }
}
#define lson o<<1,l,mid
#define rson o<<1|1,mid+1,r
int sum[MAXN<<2];
void build(int o, int l, int r) {
    if (l == r) { sum[o] = a[fp[l]]; return; }
    int mid = (l+r) >> 1;
    build(lson); build(rson);
    sum[o] = 0;
}

void pushdown(int o) {
    if (sum[o]) {
        sum[o<<1] += sum[o];
        sum[o<<1|1] += sum[o];
        sum[o] = 0;
    }
}

int query(int o, int l, int r, int v) {
    if (l == r) return sum[o];
    pushdown(o);
    int mid = (l+r) >> 1;
    if (v <= mid) return query(lson, v);
    return query(rson, v);
}

void update(int o, int l, int r, int L, int R, int v) {
    if (l >= L && r <= R) { sum[o] += v; return ; }
    pushdown(o);
    int mid = (l+r) >> 1;
    if (L <= mid) update(lson, L, R, v);
    if (R > mid) update(rson, L, R, v);
}

void change(int x, int y, int w, int n) {
    while (top[x] != top[y]) {
        if (deep[top[x]] < deep[top[y]]) swap(x, y);
        update(1, 1, n, p[top[x]], p[x], w);
        x = fa[top[x]];
    }
    if (deep[x] > deep[y]) swap(x, y);
    update(1, 1, n, p[x], p[y], w);
}

char buf[5];
int x, y, z;
int main()
{
    while (scanf("%d%d%d" , &n, &m, &Q) != EOF) {
        for (int i = 1; i <= n; i++) 
            scanf("%d", a+i);
        init();
        for (int i = 1; i <= m; i++) {
            scanf("%d%d", &x, &y);
            addedge(x, y);
            addedge(y, x);
        }
        dfs1(1, 0, 0);
        getpos(1, 1);
        build(1, 1, n);
        for (int i = 1; i <= Q; i++) {
            scanf("%s", buf);
            if (buf[0] == 'Q') {
                scanf("%d", &x);
                printf("%d\n", query(1, 1, n, p[x]));
            }
            else {
                scanf("%d%d%d", &x, &y, &z);
                if (buf[0] == 'D') z = -z;
                change(x, y, z, n);
            }
        }
    }
    return 0;
}