Union-find semi-persistente

#include <bits/stdc++.h>
using namespace std;
vector<int> pai, sub, edge;

int find(int v) {return (v == pai[v] ? v : find(pai[v]));}
void une(int x, int y, int t)
{
    x = find(x); y = find(y);
    if (x == y) return;
    if (sub[x] < sub[y]) swap(x, y);
    pai[y] = x; sub[x] += sub[y]; edge[y] = t;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int N, M, Q; cin >> N >> M >> Q;
    pai.resize(N+1); iota(pai.begin(), pai.end(), 0);
    sub.resize(N+1); fill(sub.begin(), sub.end(), 1);
    edge.resize(N+1); fill(edge.begin(), edge.end(), 0);

    for (int i = 1; i <= M; i++)
    {
        int x, y; cin >> x >> y;
        une(x, y, i);
    }

    while (Q--)
    {
        int x, y; cin >> x >> y;
        if (find(x) != find(y)) {cout << -1 << '\n'; continue;}
        int resp = 0;
        while (x != y)
        {
            if (sub[x] < sub[y]) {resp = max(resp, edge[x]); x = pai[x];}
            else {resp = max(resp, edge[y]); y = pai[y];}
        }
        cout << resp << '\n';
    }
}