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#define PROBLEM "https://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D" #include "../../template.h" #include "../count_inversions.h" void solve() { int n; cin >> n; auto a = read_vector<int> (n); cout << count_inversions(a) << endl; }
#line 1 "DP/tests/aizu_alds1_5_d_count_inversions.test.cpp" #define PROBLEM "https://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D" #line 1 "template.h" #include <bits/stdc++.h> using namespace std; #define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++) #define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--) #define REP(i,a) for(int i=0,_a=(a); i<_a; i++) #define EACH(it,a) for(__typeof(a.begin()) it = a.begin(); it != a.end(); ++it) #define DEBUG(x) { cout << #x << " = "; cout << (x) << endl; } #define PR(a,n) { cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl; } #define PR0(a,n) { cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl; } #define sqr(x) ((x) * (x)) // For printing pair, container, etc. // Copied from https://quangloc99.github.io/2021/07/30/my-CP-debugging-template.html template<class U, class V> ostream& operator << (ostream& out, const pair<U, V>& p) { return out << '(' << p.first << ", " << p.second << ')'; } template<class Con, class = decltype(begin(declval<Con>()))> typename enable_if<!is_same<Con, string>::value, ostream&>::type operator << (ostream& out, const Con& con) { out << '{'; for (auto beg = con.begin(), it = beg; it != con.end(); it++) { out << (it == beg ? "" : ", ") << *it; } return out << '}'; } template<size_t i, class T> ostream& print_tuple_utils(ostream& out, const T& tup) { if constexpr(i == tuple_size<T>::value) return out << ")"; else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); } template<class ...U> ostream& operator << (ostream& out, const tuple<U...>& t) { return print_tuple_utils<0, tuple<U...>>(out, t); } mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()); long long get_rand(long long r) { return uniform_int_distribution<long long> (0, r-1)(rng); } template<typename T> vector<T> read_vector(int n) { vector<T> res(n); for (int& x : res) cin >> x; return res; } void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); solve(); return 0; } #line 1 "Misc/compress.h" // Compressor {{{ /* Example usage: auto compressor = CompressorBuilder<T>{vs}.build(); int x = compessor.must_eq(vs[0]); compressor.compress_inplace(vs); */ // Based on https://suisen-cp.github.io/cp-library-cpp/library/util/coordinate_compressor.hpp template<typename T> struct CompressorBuilder { // Do not use directly. Use builder.build() struct Compressor { // Number of unique keys int size() const { return xs.size(); } void compress_inplace(std::vector<T>& vals) { for (int& val : vals) { val = must_eq(val); } } [[nodiscard]] std::vector<T> compress(const std::vector<T>& vals) { std::vector<T> res(vals.size()); for (int i = 0; i < static_cast<int> (res.size()); ++i) { res[i] = must_eq(vals[i]); } return res; } bool has_key(const T& key) const { return std::binary_search(xs.begin(), xs.end(), key); } #define LB(key) std::lower_bound(xs.begin(), xs.end(), key) #define UB(key) std::upper_bound(xs.begin(), xs.end(), key) std::optional<int> eq(const T& key) { auto it = LB(key); return it == xs.end() ? std::nullopt : std::optional<int>{it - xs.begin()}; } std::optional<int> geq(const T& key) { auto it = LB(key); return it == xs.end() ? std::nullopt : std::optional<int>{it - xs.begin()}; } std::optional<int> gt(const T& key) { auto it = UB(key); return it == xs.end() ? std::nullopt : std::optional<int>{it - xs.begin()}; } std::optional<int> leq(const T& key) { auto it = UB(key); return it == xs.begin() ? std::nullopt : std::optional<int>{it - xs.begin() - 1}; } std::optional<int> lt(const T& key) { auto it = LB(key); return it == xs.begin() ? std::nullopt : std::optional<int>{it - xs.begin() - 1}; } // throw exception if no such key is found int must_eq(const T& key) { auto it = LB(key); assert(it != xs.end()); return it - xs.begin(); } // throw exception if no such key is found int must_geq(const T& key) { auto it = LB(key); assert(it != xs.end()); return it - xs.begin(); } // throw exception if no such key is found int must_gt(const T& key) { auto it = UB(key); assert(it != xs.end()); return it - xs.begin(); } // throw exception if no such key is found int must_leq(const T& key) { auto it = UB(key); assert(it != xs.begin()); return it - xs.begin() - 1; } // throw exception if no such key is found int must_lt(const T& key) { auto it = LB(key); assert(it != xs.begin()); return it - xs.begin() - 1; } #undef LB #undef UB std::vector<T> xs; }; auto build() { std::sort(xs.begin(), xs.end()); xs.erase(std::unique(xs.begin(), xs.end()), xs.end()); return Compressor{xs}; } void add(const T& key) { xs.push_back(key); } void add(T&& key) { xs.push_back(std::move(key)); } std::vector<T> xs; }; // }}} #line 1 "DataStructure/Fenwick/Fenwick.h" // 1D Fenwick {{{ // 0 based index // // Tested: // - https://judge.yosupo.jp/problem/static_range_sum // - https://judge.yosupo.jp/problem/point_add_range_sum template< typename T // need to support operators + - > struct Fenwick { Fenwick(int _n) : n(_n), f(_n + 1) {} // a[u] += val void update(int u, T val) { assert(0 <= u && u < n); ++u; for (; u <= n; u += u & -u) { f[u] += val; } } // return a[0] + .. + a[u-1] T get(int u) const { assert(0 <= u && u <= n); T res = 0; for (; u > 0; u -= u & -u) { res += f[u]; } return res; } // return a[l] + .. + a[r-1] T get(int l, int r) const { assert(0 <= l && l <= r && r <= n); if (l == r) return 0; // empty return get(r) - get(l); } void reset() { std::fill(f.begin(), f.end(), T(0)); } int n; vector<T> f; }; // }}} #line 3 "DP/count_inversions.h" // Given vector vs, return number of inversions template<typename T> long long count_inversions(vector<T> vs) { int n = vs.size(); auto compressor = CompressorBuilder<T>{vs}.build(); compressor.compress_inplace(vs); Fenwick<int> bit(n); long long res = 0; for (auto v : vs) { res += bit.get(v+1, n); bit.update(v, +1); } return res; } #line 5 "DP/tests/aizu_alds1_5_d_count_inversions.test.cpp" void solve() { int n; cin >> n; auto a = read_vector<int> (n); cout << count_inversions(a) << endl; }