道路设计(Road Design) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

#include <iostream>
#include <vector>
#include <numeric>
#include <algorithm>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m;
    if (!(cin >> n >> m)) return 0;
    vector<int> p(n + 1), sz(n + 1, 1);
    iota(p.begin(), p.end(), 0);
    auto find = [&](int x) {
        while (p[x] != x) x = p[x];
        return x;
    };
    vector<pair<int, int>> history;
    history.reserve(m);
    for (int i = 0; i < m; ++i) {
        int op;
        cin >> op;
        if (op == 1) {
            int u, v;
            cin >> u >> v;
            int ru = find(u), rv = find(v);
            if (ru == rv) {
                history.push_back({0, 0});
            } else {
                if (sz[ru] > sz[rv]) swap(ru, rv);
                p[ru] = rv;
                sz[rv] += sz[ru];
                history.push_back({ru, rv});
            }
        } else if (op == 2) {
            if (!history.empty()) {
                auto [ru, rv] = history.back();
                history.pop_back();
                if (ru != 0) {
                    p[ru] = ru;
                    sz[rv] -= sz[ru];
                }
            }
        } else {
            int u, v;
            cin >> u >> v;
            if (find(u) == find(v)) cout << "Yes\n";
            else cout << "No\n";
        }
    }
    return 0;
}