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Educational Codeforces Round 160 (Rated for Div. 2)/D. Array Collapse.cpp

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+/* Problem URL: https://codeforces.com/contest/1913/problem/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;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        int n;
+        cin >> n;
+
+        vl fds(n);
+        cin >> fds;
+
+        stack<pair<int, int>> s;
+
+        vi left(n, 0);
+        vi right(n, n - 1);
+
+        rep(i, n) {
+            while (!s.empty() && s.top().first > fds[i]) {
+                s.pop();
+            }
+
+            if (s.empty()) {
+                s.emplace(fds[i], i + 1);
+                continue;
+            }
+
+            left[i] = s.top().second;
+            s.emplace(fds[i], i);
+        }
+
+        s = stack<pair<int, int>>();
+
+        for (int i = n - 1; i >= 0; i--) {
+            while (!s.empty() && s.top().first > fds[i]) {
+                s.pop();
+            }
+
+            if (s.empty()) {
+                s.emplace(fds[i], i - 1);
+                continue;
+            }
+
+            right[i] = s.top().second;
+            s.emplace(fds[i], i);
+        }
+
+        vl dp1(n + 1);
+        dp1[0] = 1;
+
+        vl dp2(n + 1);
+        dp2[n] = 1;
+
+        const ll mod = 998244353;
+
+        rep(i, n) {
+            if (left[i] > 0) {
+                dp1[i + 1] += dp1[i];
+                continue;
+            }
+
+            dp1[i + 1] = (dp1[i] + i) % mod;
+        }
+
+        for (int i = n - 1; i >= 0; i--) {
+            if (right[i] < n - 1) {
+                dp2[i] += dp2[i + 1];
+                continue;
+            }
+
+            dp2[i] = (dp2[i] + (n - i + 1)) % mod;
+        }
+
+        cout << dp1[n] + dp2[0] << '\n';
+    }
+}