HDU 3966 Aragorn's Story (树链点权剖分，成段修改单点查询)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3966

树链剖分的模版，成段更新单点查询。熟悉线段树的成段更新的话就小case啦。

//树链剖分 边权修改 单点查询
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
using namespace std;
const int MAXN = 5e4 + 10;
struct data {
    int to , next;
}edge[MAXN << 1];
int head[MAXN] , cnt , tot;
int top[MAXN] , par[MAXN] , son[MAXN] , size[MAXN] , dep[MAXN];
int id[MAXN] , fid[MAXN]; //id[i]表示i对应在线段树上的位置 fid[i]表示线段树位置是i的叶子 对应的节点 
int a[MAXN];

void init() {
    tot = cnt = 0;
    memset(head , -1 , sizeof(head));
}

inline void add(int u , int v) {
    edge[tot].next = head[u];
    edge[tot].to = v;
    head[u] = tot++;
}

void dfs1(int u , int p , int d) {
    dep[u] = d , size[u] = 1 , son[u] = u , par[u] = p;
    for(int i = head[u] ; ~i ; i = edge[i].next) {
        int v = edge[i].to;
        if(v == p)
            continue;
        dfs1(v , u , d + 1);
        if(size[v] >= size[son[u]] || son[u] == u)
            son[u] = v;
        size[u] += size[v];
    }
}

void dfs2(int u , int p , int t) {
    top[u] = t , id[u] = ++cnt;
    fid[cnt] = u;
    if(son[u] != u)
        dfs2(son[u] , u , t);
    for(int i = head[u] ; ~i ; i = edge[i].next) {
        int v = edge[i].to;
        if(v == p || v == son[u])
            continue;
        dfs2(v , u , v);
    }
}

struct segtree {
    int l , r;
    int sum;
}T[MAXN << 2];

void pushup(int p) {
    if(T[p].sum != 0) {
        int ls = p << 1 , rs = (p << 1)|1;
        T[ls].sum += T[p].sum;
        T[rs].sum += T[p].sum;
        T[p].sum = 0;
    }
}

void build(int p , int l , int r) {
    int mid = (l + r) >> 1;
    T[p].l = l , T[p].r = r;
    T[p].sum = 0;
    if(l == r) {
        T[p].sum = a[fid[l]]; //
        return ;
    }
    build(p << 1 , l , mid);
    build((p << 1)|1 , mid + 1 , r);
}

void updata(int p , int l , int r , int num) {
    int mid = (T[p].l + T[p].r) >> 1;
    if(T[p].l == l && T[p].r == r) {
        T[p].sum += num;
        return ;
    }
    pushup(p);
    if(r <= mid) {
        updata(p << 1 , l , r , num);
    }
    else if(l > mid) {
        updata((p << 1)|1 , l , r , num);
    }
    else {
        updata(p << 1 , l , mid , num);
        updata((p << 1)|1 , mid + 1 , r , num);
    }
}

int query(int p , int pos) {
    int mid = (T[p].l + T[p].r) >> 1;
    if(T[p].l == T[p].r && T[p].r == pos) {
        return T[p].sum;
    }
    pushup(p);
    if(pos <= mid) {
        return query(p << 1 , pos);
    }
    else {
        return query((p << 1)|1 , pos);
    }
}

void change(int u , int v , int num) {
    int fu = top[u] , fv = top[v];
    int sum = 0;
    while(fu != fv) {
        if(dep[fu] > dep[fv]) {
            updata(1 , id[fu] , id[u] , num);
            u = par[fu];
            fu = top[u];
        }
        else {
            updata(1 , id[fv] , id[v] , num);
            v = par[fv];
            fv = top[v];
        }
    }
    if(dep[u] >= dep[v]) {
        updata(1 , id[v] , id[u] , num);
    }
    else {
        updata(1 , id[u] , id[v] , num);
    }
}

int main()
{
    int n , u , v , m , xx;
    while(~scanf("%d %d %d" , &n , &xx , &m)) {
        init();
        for(int i = 1 ; i <= n ; ++i) {
            scanf("%d" , a + i);
        }
        for(int i = 1 ; i < n ; ++i) {
            scanf("%d %d" , &u , &v);
            add(u , v);
            add(v , u);
        }
        cnt = 0;
        dfs1(1 , 1 , 0);
        dfs2(1 , 1 , 1);
        build(1 , 1 , cnt);
        char q[10];
        while(m--) {
            scanf("%s" , q);
            if(q[0] == 'Q') {
                scanf("%d" , &xx);
                printf("%d
" , query(1 , id[xx]));
            }
            else if(q[0] == 'I') {
                scanf("%d %d %d" , &u , &v , &xx);
                change(u , v , xx);
            }
            else {
                scanf("%d %d %d" , &u , &v , &xx);
                change(u , v , -xx);
            }
        }
    }
    return 0;
}