題目連結

  一道樹鏈剖分的基礎題，我的做法可能與廣大網友不大一樣，我將邊也算做是一個點，然後相當於是把兩個端點相互連線在邊所代表的那個點上，這樣更新邊就變成了更新點，查詢就是區間查詢。

  一開始讀了道假題做了半天（最近總是在讀假題……），還以為是區間和，然後看到區間邊長最大值的時候，我整個人都奔潰了！！！

#include <iostream>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <algorithm>
#include <limits>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#define lowbit(x) ( x&(-x) )
#define pi 3.141592653589793
#define e 2.718281828459045
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
const int maxN = 20005;
const ll INF = 1e9 + 7;
int N, cnt, head[maxN], root[maxN], depth[maxN], size[maxN], W_son[maxN], tot, topy[maxN], id[maxN], num;
ll a[maxN], tree[maxN<<2], new_a[maxN];
struct Eddge
{
    int nex, to;
    Eddge(int a=-1, int b=0):nex(a), to(b) {}
}edge[maxN<<1];
void addEddge(int u, int v)
{
    edge[cnt] = Eddge(head[u], v);
    head[u] = cnt++;
}
void dfs1(int u, int fa, int deep)
{
    root[u] = fa;
    depth[u] = deep;
    size[u] = 1;
    for(int i=head[u]; i!=-1; i=edge[i].nex)
    {
        int v = edge[i].to;
        if(v == fa) continue;
        dfs1(v, u, deep+1);
        size[u] += size[v];
        if(size[W_son[u]] < size[v])
        {
            W_son[u] = v;
        }
    }
}
void dfs2(int u, int top)
{
    topy[u] = top;
    id[u] = ++num;
    new_a[num] = a[u];
    if(!W_son[u]) return;
    dfs2(W_son[u], top);
    for(int i=head[u]; i!=-1; i=edge[i].nex)
    {
        int v = edge[i].to;
        if(v == root[u] || v == W_son[u]) continue;
        dfs2(v, v);
    }
}
void buildTree(int rt, int l, int r)
{
    if(l == r)
    {
        tree[rt] = new_a[l];
        return;
    }
    int mid = (l + r)>>1;
    buildTree(rt<<1, l, mid);
    buildTree(rt<<1|1, mid+1, r);
    tree[rt] = max(tree[rt<<1], tree[rt<<1|1]);
}
void update(int rt, int l, int r, int qx, ll val)
{
    if(l == r)
    {
        tree[rt] = val;
        return;
    }
    int mid = (l + r)>>1;
    if(qx<=mid) update(rt<<1, l, mid, qx, val);
    else update(rt<<1|1, mid+1, r, qx, val);
    tree[rt] = max(tree[rt<<1], tree[rt<<1|1]);
}
ll query(int rt, int l, int r, int ql, int qr)
{
    if(ql<=l && qr>=r) return tree[rt];
    int mid = (l + r)>>1;
    if(ql>mid) return query(rt<<1|1, mid+1, r, ql, qr);
    else if(qr<=mid) return query(rt<<1, l, mid, ql, qr);
    else return max( query(rt<<1, l, mid, ql, qr), query(rt<<1|1, mid+1, r, ql, qr) );
}
void update_Point(int x, ll val) { update(1, 1, tot, id[x], val); }
ll query_Range(int x, int y)
{
    ll ans = -INF;
    while(topy[x] != topy[y])
    {
        if(depth[topy[x]] < depth[topy[y]]) swap(x, y);
        ans = max(ans, query(1, 1, tot, id[topy[x]], id[x]));
        x = root[topy[x]];
    }
    if(depth[x] > depth[y]) swap(x, y);
    ans = max(ans, query(1, 1, tot, id[x], id[y]));
    return ans;
}
void init()
{
    memset(W_son, 0, sizeof(W_son));
    memset(head, -1, sizeof(head));
    cnt = num = 0;    tot = 2*N-1;
    for(int i=0; i<maxN; i++) a[i] = -INF;
}
int main()
{
    int T;  scanf("%d", &T);
    while(T--)
    {
        scanf("%d", &N);
        init();
        for(int i=1; i<N; i++)
        {
            int e1, e2; ll e3;
            scanf("%d%d%lld", &e1, &e2, &e3);
            a[N+i] = e3;
            addEddge(e1, N+i);
            addEddge(N+i, e1);
            addEddge(N+i, e2);
            addEddge(e2, N+i);
        }
        dfs1(1, 1, 0);
        dfs2(1, 1);
        buildTree(1, 1, tot);
        char s[20];
        while(scanf("%s", s) && s[0]!='D')
        {
            if(s[0] == 'C')
            {
                int e1;
                ll e2;
                scanf("%d%lld", &e1, &e2);
                update_Point(N+e1, e2);
            }
            else
            {
                int e1, e2;
                scanf("%d%d", &e1, &e2);
                printf("%lld\n", query_Range(e1, e2));
            }
        }
    }
    return 0;
}