Add a lot more problems and a TODO list

ITMO Academy: pilot course - Disjoint Sets Union - Step 3/A. DSU with rollback.cpp

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+/* Problem URL: https://codeforces.com/edu/course/2/lesson/7/3/practice/contest/289392/problem/A */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n, m;
+    cin >> n >> m;
+
+    vi dsu(n);
+    vi size(n);
+    rep(i, n) {
+        dsu[i] = i;
+        size[i] = 1;
+    }
+
+    stack<pair<int, int>> re;
+
+    function<int(int)> find_p = [&](int i) {
+        if (dsu[i] == i) {
+            return i;
+        }
+        return find_p(dsu[i]);
+    };
+
+    int c = n;
+
+    auto join = [&](int a, int b) {
+        a = find_p(a);
+        b = find_p(b);
+
+        if (a == b) {
+            return;
+        }
+
+        if (size[a] < size[b]) {
+            swap(a, b);
+        }
+
+        re.emplace(a, b);
+        dsu[b] = a;
+
+        if (size[a] == size[b]) {
+            size[a]++;
+        }
+
+        c--;
+    };
+
+    auto rollback = [&]() {
+        while (re.top().first != -1) {
+            auto [a, b] = re.top();
+            re.pop();
+
+            if (size[b] == size[a] - 1) {
+                size[a]--;
+            }
+
+            dsu[b] = b;
+            c++;
+        }
+        re.pop();
+    };
+
+    while (m--) {
+        string op;
+        cin >> op;
+
+        if (op[0] == 'u') {
+            int a, b;
+            cin >> a >> b;
+            join(a - 1, b - 1);
+            cout << c << '\n';
+            continue;
+        }
+
+        if (op[0] == 'p') {
+            re.emplace(-1, -1);
+            continue;
+        }
+
+        rollback();
+        cout << c << '\n';
+    }
+}