Northern Eurasia Finals Online 2020 L

处理了一年的边界问题

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
#define fi first
#define se second
#define sz(v) ((int)(v).size())
#define debug(a) cout << #a << " = " << a << endl;
typedef long long ll;
typedef pair <int, int> P;
const ll MOD = 1e9 + 7;
string arr[N];
map < string, vector < int > > mp;
priority_queue < int, vector < int >, greater < int > > Q;
struct node {
    int l, r, k;
} tree[N];
int d[N], f[N], sz[N], hs[N];
void dfs1(int u, int fa, int dep) {
    if (!u)    return ;
    d[u] = dep; f[u] = fa; sz[u] = 1;
    dfs1(tree[u].l, u, dep + 1);
    dfs1(tree[u].r, u, dep + 1);
    sz[u] += sz[tree[u].l] + sz[tree[u].r];
    if (tree[u].l == tree[u].r && tree[u].l == 0)    return ;
    hs[u] = sz[tree[u].l] > sz[tree[u].r] ? tree[u].l : tree[u].r;
}

int top[N];
void dfs2(int u, int T) {
    if (!u)    return ;
    top[u] = T;
    if (!hs[u])    return ;
    dfs2(hs[u], T);
    if (hs[u] != tree[u].l) dfs2(tree[u].l, tree[u].l);
    else dfs2(tree[u].r, tree[u].r);
}

int Lca(int u, int v) {
    while (top[u] != top[v]) {
        if (d[top[u]] < d[top[v]])    swap(u, v);
        u = f[top[u]];
    }
    return  d[u] > d[v] ? v : u;
}

vector < P > len;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> tree[i].l >> tree[i].r >> tree[i].k;
        len.emplace_back(tree[i].k, i);
    }
    int q; cin >> q;
    sort(len.begin(), len.end());
    dfs1(1, 0, 0); dfs2(1, -1);
    while (q--) {
        int L, R, l, r; cin >> L >> R;
        if ((L <= len.front().fi && R >= len.back().fi) || R < len.front().fi || L > len.back().fi) {
            cout << "1" << endl;
            continue;
        } 
        auto pos1 = lower_bound(len.begin(), len.end(), P(L, 0));
        if (pos1 == len.end())    pos1--, l = (*pos1).se;  
        else if (pos1 != len.begin()) {
            int x1 = (*pos1).se;
            pos1--; int x2 = (*pos1).se;
            l = Lca(x1, x2);
        }
        else l = (*pos1).se;
        auto pos2 = upper_bound(len.begin(), len.end(), P(R, 10000000));
        if (pos2 == len.begin())    r = (*pos2).se;  
        else if (pos2 != len.end()) {
            int x1 = (*pos2).se;
            pos2--; int x2 = (*pos2).se;
            r = Lca(x1, x2);
        }
        else pos2--, r = (*pos2).se;
        int lca = Lca(l, r);
        if (L <= len.front().fi) {
            cout << d[r] * 2 + 3 << endl;
            continue;
        }
        if (R >= len.back().fi) {
            cout << d[l] * 2 + 3 << endl;
            continue;
        }
        int ans = d[lca] * 2 + 1;
        ans += (d[l] - d[lca]) * 2 + (d[r] - d[lca]) * 2 + 2; 
        cout << ans << endl; 
    }    
    return 0;
}