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2024-2025 ICPC, NERC, Northern Eurasia Finals (Unrated, Online Mirror, ICPC Rules, Teams Preferred)/A. Adrenaline Rush.cpp

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+/* Problem URL: https://codeforces.com/problemset/problem/2052/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;
+}
+
+const int oo = INT32_MAX >> 1;
+const ll OO = INT64_MAX >> 1;
+
+
+void pre()
+{
+
+}
+
+#define TEST 0
+
+void solve()
+{
+    int n;
+    cin >> n;
+    vi p(n);
+    cin >> p;
+    reverse(all(p));
+
+    V<pair<int, int>> ans;
+    V<bool> us(n + 1);
+
+    // rep(i, n) {
+    //     int c = p[i];
+    //     for (int j = c - 1; j > 0; j--) {
+    //         if (us[j - 1]) {
+    //             continue;
+    //         }
+    //
+    //         ans.emplace_back(c, j);
+    //     }
+    //
+    //     for (int j = c + 1; j <= n; j++) {
+    //         if (us[j - 1]) {
+    //             continue;
+    //         }
+    //
+    //         ans.emplace_back(j, c);
+    //         ans.emplace_back(c, j);
+    //     }
+    // }
+
+    rep(i, n) {
+        int c = p[i];
+        us[c] = true;
+
+        for (int j = c - 1; j > 0; j--) {
+            if (us[j]) {
+                continue;
+            }
+            ans.emplace_back(c, j);
+        }
+
+        for (int j = 1; j <= n; j++) {
+            if (us[j]) {
+                continue;
+            }
+            ans.emplace_back(j, c);
+        }
+    }
+
+    cout << ans.size() << '\n';
+    repv(i, ans) {
+        cout << i.first << ' ' << i.second << '\n';
+    }
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    pre();
+
+    int t;
+    (TEST && cin >> t) || (t = 1);
+    while (t--) {
+        solve();
+    }
+}