Add some more problems and update TODO list

Codeforces Round 898 (Div. 4)/H. Mad City.cpp

@@ -0,0 +1,221 @@
+/* Problem URL: https://codeforces.com/problemset/problem/1873/H */
+
+#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;
+}
+
+const int oo = INT32_MAX >> 1;
+const ll OO = INT64_MAX >> 1;
+
+
+void pre()
+{
+
+}
+
+#define TEST 1
+
+void solve()
+{
+    int n, a, b;
+    cin >> n >> a >> b;
+    a--, b--;
+
+    vi dsu(n);
+    rep(i, n) {
+        dsu[i] = i;
+    }
+
+    function<int(int)> find_p = [&](int i) {
+        if (dsu[i] == i) {
+            return dsu[i];
+        }
+        return dsu[i] = find_p(dsu[i]);
+    };
+
+    auto join = [&](int a, int b) {
+        a = find_p(a);
+        b = find_p(b);
+        dsu[b] = a;
+        return a == b;
+    };
+
+    vi loop;
+    pair<int, int> edge;
+
+    vvi graph(n);
+    rep(i, n) {
+        int u, v;
+        cin >> u >> v;
+        u--, v--;
+
+        if (!join(u, v)) {
+            graph[u].push_back(v);
+            graph[v].push_back(u);
+            continue;
+        }
+
+        edge = {u, v};
+    }
+
+    vi depth(n, -1);
+    vi parent(n);
+
+    function<void(int, int)> dfs = [&](int i, int p) {
+        depth[i] = depth[p] + 1;
+        parent[i] = p;
+
+        repv(j, graph[i]) {
+            if (j == p) {
+                continue;
+            }
+
+            dfs(j, i);
+        }
+    };
+
+    dfs(0, 0);
+
+    int u = edge.first;
+    int v = edge.second;
+
+    if (depth[u] > depth[v]) {
+        swap(u, v);
+    }
+
+    int diff = depth[v] - depth[u];
+    while (diff--) {
+        loop.push_back(v);
+        v = parent[v];
+    }
+
+    while (u != v) {
+        loop.push_back(u);
+        loop.push_back(v);
+
+        u = parent[u];
+        v = parent[v];
+    }
+    loop.push_back(u);
+
+    graph[edge.first].push_back(edge.second);
+    graph[edge.second].push_back(edge.first);
+
+    vi disa(n, oo);
+    vi disb(n, oo);
+
+    auto bfs = [&](int ini, vi &dis) {
+        dis[ini] = 0;
+        queue<int> q;
+        q.push(ini);
+
+        while (!q.empty()) {
+            auto i = q.front();
+            q.pop();
+
+            repv(j, graph[i]) {
+                if (dis[j] > dis[i] + 1) {
+                    dis[j] = dis[i] + 1;
+                    q.push(j);
+                }
+            }
+        }
+    };
+
+    bfs(a, disa);
+    bfs(b, disb);
+
+    repv(i, loop) {
+        if (disa[i] > disb[i]) {
+            cout << "YES\n";
+            return;
+        }
+    }
+
+    cout << "NO\n";
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    pre();
+
+    int t;
+    (TEST && cin >> t) || (t = 1);
+    while (t--) {
+        solve();
+    }
+}