#line 1 "graph/cartesian_tree.yukicoder-1031.test.cpp" #define PROBLEM "https://yukicoder.me/problems/no/1031" #line 2 "utils/macros.hpp" #define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i)) #define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++ (i)) #define REP_R(i, n) for (int i = (int)(n) - 1; (i) >= 0; -- (i)) #define REP3R(i, m, n) for (int i = (int)(n) - 1; (i) >= (int)(m); -- (i)) #define ALL(x) std::begin(x), std::end(x) #line 2 "graph/cartesian_tree.hpp" #include #include #line 5 "graph/cartesian_tree.hpp" /** * @brief Cartesian tree ($O(n)$) * @note the smallest value is the root * @note if a is not distinct, the way for tie-break is undefined * @return the binary tree as the list of parents */ template > std::vector construct_cartesian_tree(const std::vector & a, const Comparator & cmp = Comparator()) { int n = a.size(); std::vector parent(n, -1); REP3 (i, 1, n) { int p = i - 1; // parent of i int l = -1; // left child of i while (p != -1 and cmp(a[i], a[p])) { int pp = parent[p]; // parent of parent of i if (l != -1) { parent[l] = p; } parent[p] = i; l = p; p = pp; } parent[i] = p; } return parent; } #line 2 "graph/format.hpp" #include #include #line 6 "graph/format.hpp" std::pair >, int> children_from_parent(const std::vector & parent) { int n = parent.size(); std::vector > children(n); int root = -1; REP (x, n) { if (parent[x] == -1) { assert (root == -1); root = x; } else { children[parent[x]].push_back(x); } } assert (root != -1); return std::make_pair(children, root); } std::vector > adjacent_list_from_children(const std::vector > & children) { int n = children.size(); std::vector > g(n); REP (x, n) { for (int y : children[x]) { g[x].push_back(y); g[y].push_back(x); } } return g; } #line 2 "utils/greedily_increasing_subsequence.hpp" #include #include #line 5 "data_structure/sparse_table.hpp" /** * @brief Sparse Table (idempotent monoid) * @note the unit is required just for convenience * @note $O(N \log N)$ space */ template struct sparse_table { typedef typename IdempotentMonoid::value_type value_type; std::vector > table; IdempotentMonoid mon; sparse_table() = default; /** * @note $O(N \log N)$ time */ template sparse_table(InputIterator first, InputIterator last, const IdempotentMonoid & mon_ = IdempotentMonoid()) : mon(mon_) { table.emplace_back(first, last); int n = table[0].size(); int log_n = 32 - __builtin_clz(n); table.resize(log_n, std::vector(n)); REP (k, log_n - 1) { REP (i, n) { table[k + 1][i] = i + (1ll << k) < n ? mon.mult(table[k][i], table[k][i + (1ll << k)]) : table[k][i]; } } } /** * @note $O(1)$ */ value_type range_get(int l, int r) const { if (l == r) return mon.unit(); // if there is no unit, remove this line assert (0 <= l and l < r and r <= (int)table[0].size()); int k = 31 - __builtin_clz(r - l); // log2 return mon.mult(table[k][l], table[k][r - (1ll << k)]); } }; #line 2 "monoids/min.hpp" #include #include template struct min_monoid { typedef T value_type; value_type unit() const { return std::numeric_limits::max(); } value_type mult(value_type a, value_type b) const { return std::min(a, b); } }; #line 9 "utils/greedily_increasing_subsequence.hpp" /** * @brief Length of Greedily Increasing Subsequences (前処理 $O(n \log n)$ + $O(1)$) * @description computes the lengths of the greedily increasing subsubsequence for the given interval * @note the greedily increasing subsubsequence for a sequence $a$ means the subsubsequence of the elements $a_i$ which satisfy $\forall j \lt i. a_j \lt a_i$. */ class greedily_increasing_subsequence { std::vector depth; sparse_table > table; public: greedily_increasing_subsequence() = default; int operator () (int l, int r) const { assert (0 <= l and l <= r and r <= (int)depth.size()); if (l == r) return 0; return depth[l] - table.range_get(l, r) + 1; } private: greedily_increasing_subsequence(const std::vector & depth_) : depth(depth_), table(ALL(depth_)) { } public: /** * @note this is just a constructor, but is needed to specify template arguments. */ template , class RandomAccessIterator> static greedily_increasing_subsequence construct(RandomAccessIterator first, RandomAccessIterator last, const Comparator & cmp = Comparator()) { int n = std::distance(first, last); // make a forest std::vector parent(n, -1); std::stack stk; REP (i, n) { while (not stk.empty() and cmp(*(first + stk.top()), *(first + i))) { parent[stk.top()] = i; stk.pop(); } stk.push(i); } // calculate depths std::vector depth(n); REP_R (i, n) { if (parent[i] != -1) { depth[i] = depth[parent[i]] + 1; } } return greedily_increasing_subsequence(depth); } }; #line 6 "graph/cartesian_tree.yukicoder-1031.test.cpp" #include #line 10 "graph/cartesian_tree.yukicoder-1031.test.cpp" #include using namespace std; int64_t solve1(int n, const vector & p) { // prepare a data structure for the sequence auto f = greedily_increasing_subsequence::construct(ALL(p)); // construct the Cartesian tree vector parent = construct_cartesian_tree(p); vector > children; int root; tie(children, root) = children_from_parent(parent); // fold the Cartesian tree int64_t ans = 0; auto go = [&](auto && go, int l, int m, int r) -> void { if (l == r) { return; } ans += f(m + 1, r); for (int x : children[m]) { if (x < m) { go(go, l, x, m); } else { go(go, m + 1, x, r); } } }; go(go, 0, root, n); return ans; } int64_t solve(int n, vector p) { int64_t ans = solve1(n, p); reverse(ALL(p)); return ans + solve1(n, p); } int main() { int n; scanf("%d", &n); vector p(n); REP (i, n) { scanf("%d", &p[i]); } long long ans = solve(n, p); printf("%lld\n", ans); return 0; }