LightOJ 1348 Aladdin and the Return Journey

题意：

给出N个节点的一棵树，每个节点有一个权值。

有两种操作：

1)      0 i j, 问节点i->节点j的路上的总权值。

2)      1 i v, 把节点i的权值改变成v。

思路：

权值在点上的树链剖分+线段树单点更新+线段树成段询问

#include <iostream>
#include <cstring>
#include <string>
#include <cstdio>
#include <vector>
using namespace std;
int n, q;
#define maxn 30010
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
int siz[maxn], top[maxn], fa[maxn], son[maxn], dep[maxn];
int w[maxn], fw[maxn];
int A[maxn];
vector <int> mp[maxn];
int pos;
int sum[maxn<<2];
void PushUp(int rt)
{
    sum[rt] = sum[rt<<1] + sum[rt<<1|1];
}
void build(int l, int r, int rt)
{
    sum[rt] = 0;
    if(l == r)
    {
        sum[rt] = A[fw[l]];
        return;
    }
    int m = (l+r)>>1;
    build(lson);
    build(rson);
    PushUp(rt);
}
void update(int p, int val, int l, int r, int rt)
{
    if(l == r)
    {
        sum[rt] = val;
        return;
    }
    int m = (l+r)>>1;
    if(p <= m) update(p, val, lson);
    else update(p, val, rson);
    PushUp(rt);
}
int query_sum(int L, int R, int l, int r, int rt)
{
    if(L <= l && R >= r)
    {
        return sum[rt];
    }
    int m = (l+r)>>1;
    int ret = 0;
    if(L <= m) ret += query_sum(L, R, lson);
    if(R > m) ret += query_sum(L, R, rson);
    return ret;
}
int dfs1(int u, int pre, int deep)
{
    siz[u] = 1; dep[u] = deep; fa[u] = pre;
    int mmax = 0;
    for(int i = 0; i < mp[u].size(); i++)
    {
        if(mp[u][i] != pre)
        {
            int temp = dfs1(mp[u][i], u, deep+1);
            siz[u] += temp;
            if(son[u] == -1 || temp >= mmax) 
            {
                son[u] = mp[u][i];
                mmax = temp;
            }
        }
    }
    return siz[u];
}
void dfs2(int u, int val)
{
    top[u] = val;
    if(son[u] != -1)
    {
        w[u] = ++pos;
        fw[w[u]] = u;
        dfs2(son[u], val);
    }
    else if(son[u] == -1)
    {
        w[u] = ++pos;
        fw[w[u]] = u;
        return;
    }
    for(int i = 0; i < mp[u].size(); i++)
    {        
        if(mp[u][i] != son[u] && mp[u][i] != fa[u]) dfs2(mp[u][i], mp[u][i]);
    }
}
int find_sum(int u, int v)
{
    int f1 = top[u], f2 = top[v];
    int temp = 0;
    while(f1 != f2)
    {
        if(dep[f1] < dep[f2])
        {
            swap(f1, f2); 
            swap(u, v);
        }
        temp += query_sum(w[f1], w[u], 1, pos, 1);
        u = fa[f1]; f1 = top[u];
    }
    if(dep[u] > dep[v]) swap(u, v);
    temp += query_sum(w[u], w[v], 1, pos, 1);
    return temp;
}
int main() 
{
  //  freopen("in.txt", "r", stdin);
    int T;
    scanf("%d", &T);
    int cast = 0;
    while(T--)
    {
        scanf("%d", &n);
        cast++;
        for(int i = 1; i <= n; i++) mp[i].clear(); 
        pos = 0;
        memset(son, -1, sizeof(son));
        for(int i = 1; i <= n; i++) scanf("%d", &A[i]);
        for(int i = 1; i <= n-1; i++)
        {
            int a, b; scanf("%d%d", &a, &b);
            a++; b++;
            mp[a].push_back(b);
            mp[b].push_back(a);
        }
        dfs1(1, -1, 1);
        dfs2(1, 1);
        build(1, pos, 1);
        
        scanf("%d", &q);
        int op;
        printf("Case %d:
", cast);
        while(q--)
        {
            scanf("%d", &op);
            int u, v; 
            scanf("%d%d", &u, &v);
            if(op == 1) update(w[u+1], v, 1, pos, 1);
            else if(op == 0) printf("%d
", find_sum(u+1, v+1));
        }
        
    }
    return 0;
}