Add a lot more of my solutions.

I don't remember which ones doesn't pass though

CSES Problem Set/Flight Routes Check.cpp

@@ -0,0 +1,149 @@
+/* Problem URL: https://cses.fi/problemset/task/1682 */
+
+#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;
+
+    vvi graph(n);
+    vvi inv(n);
+
+    while (m--) {
+        int a, b;
+        cin >> a >> b;
+        a--, b--;
+
+        graph[a].push_back(b);
+        inv[b].push_back(a);
+    }
+
+    V<bool> vis(n);
+    stack<int> s;
+
+    function<void(int)> postorder = [&](int i) {
+        vis[i] = true;
+
+        for (auto j : graph[i]) {
+            if (vis[j]) {
+                continue;
+            }
+
+            postorder(j);
+        }
+
+        s.push(i);
+    };
+
+    rep(i, n) {
+        if (vis[i]) {
+            continue;
+        }
+
+        postorder(i);
+    }
+
+    int choice = s.top();
+    fill(all(vis), false);
+
+    function<void(int)> dfs = [&](int i) {
+        vis[i] = true;
+
+        for (auto j : inv[i]) {
+            if (vis[j]) {
+                continue;
+            }
+
+            dfs(j);
+        }
+    };
+
+    dfs(choice);
+
+    rep(i, n) {
+        if (!vis[i]) {
+            cout << "NO\n";
+            cout << i + 1 << ' ' << choice + 1 << '\n';
+            return 0;
+        }
+    }
+
+    cout << "YES\n";
+}