A bunch new problems

Codeforces Round 1065 (Div. 3)/D. Rae Taylor and Trees (easy version).cpp

@@ -0,0 +1,143 @@
+/* Problem URL: https://codeforces.com/problemset/problem/2171/D */
+
+#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;
+    cin >> n;
+    vi p(n);
+    cin >> p;
+
+    vi suf(n + 1);
+    vi pos(n);
+    for (int i = n - 1; i >= 0; i--) {
+        suf[i] = max(suf[i + 1], p[i]);
+        pos[p[i] - 1] = i;
+    }
+
+    int now = 1;
+    int ma = 1;
+    int lim = n;
+    while (now <= n) {
+        int po = pos[now - 1];
+        if (po >= lim) {
+            now++;
+            continue;
+        }
+
+        if (now > ma) {
+            cout << "No\n";
+            return;
+        }
+
+        rmax(ma, suf[po]);
+        rmin(lim, po);
+        now++;
+    }
+
+    if (lim != 0) {
+        cout << "No\n";
+        return;
+    }
+
+    cout << "Yes\n";
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    pre();
+
+    int t;
+    (TEST && cin >> t) || (t = 1);
+    while (t--) {
+        solve();
+    }
+}

Codeforces Round 1065 (Div. 3)/F. Rae Taylor and Trees (hard version).cpp

@@ -93,42 +93,52 @@ void solve()
     vi p(n);
     cin >> p;
 
+    vi suf(n + 1);
     vi pos(n);
-    rep(i, n) {
+    for (int i = n - 1; i >= 0; i--) {
+        suf[i] = max(suf[i + 1], p[i]);
         pos[p[i] - 1] = i;
     }
 
-    stack<pair<int, int>> s;
+    V<pair<int, int>> ans;
 
-    pair<int, int> big = {0, 0};
-
-    V<pair<int, int>> edges;
-
-    for (int i = n - 1; i >= 0; i--) {
-        while (!s.empty() && s.top().first > pos[i]) {
-            edges.emplace_back(s.top().second + 1, i + 1);
-            s.pop();
+    int now = 1;
+    int lim = n;
+    int ma = 1;
+    while (now < n) {
+        int ps = pos[now - 1];
+        if (now > ma) {
+            cout << "No\n";
+            return;
         }
 
-        if (big.first > pos[i]) {
-            edges.emplace_back(big.second + 1, i + 1);
+        if (ps >= lim) {
+            now++;
             continue;
         }
 
-        big = {pos[i], i};
-        s.emplace(pos[i], i);
+        nrep(i, ps + 1, n) {
+            if (p[i] < now) {
+                break;
+            }
+
+            ans.emplace_back(p[i], now);
+        }
+        if (now != ma) {
+            ans.emplace_back(ma, now);
+        }
+
+        lim = ps;
+        rmax(ma, suf[ps]);
     }
 
-    sortv(edges);
-    edges.erase(unique(all(edges)), edges.end());
-
-    if (edges.size() != n - 1) {
+    if (ans.size() < n - 1) {
         cout << "No\n";
         return;
     }
 
     cout << "Yes\n";
-    repv(i, edges) {
+    repv(i, ans) {
         cout << i.first << ' ' << i.second << '\n';
     }
 }