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- #include <iostream>
- #include <vector>
- #include <string>
- #include <iomanip>
- #include <queue>
- #include <cmath>
- #include <algorithm>
- #include <tuple>
- #include <iomanip>
- #include <stdio.h>
- #include <numeric>
- #include <map>
- #include <bitset>
- #include <set>
- #include <stack>
- #include <queue>
- #include <unordered_set>
- //#pragma GCC optimize("Ofast,no-stack-protector")
- #pragma GCC optimize("O3")
- //#pragma GCC target("avx2")
- //#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
- //#pragma GCC optimize("unroll-loops")
- //#pragma GCC optimize("fast-math")
- //#pragma GCC optimize("section-anchors")
- //#pragma GCC optimize("profile-values,profile-reorder-functions,tracer")
- //#pragma GCC optimize("vpt")
- //#pragma GCC optimize("rename-registers")
- //#pragma GCC optimize("move-loop-invariants")
- //#pragma GCC optimize("unswitch-loops")
- //#pragma GCC optimize("function-sections")
- //#pragma GCC optimize("data-sections")
- //#pragma GCC optimize("branch-target-load-optimize")
- //#pragma GCC optimize("branch-target-load-optimize2")
- //#pragma GCC optimize("btr-bb-exclusive")
- #define int long long
- #define ll long long
- #define ull unsigned long long
- #define all(a) a.begin(), a.end()
- #define pii pair<int, int>
- #define pb push_back
- #define ld long double
- using namespace std;
- //const int INF = 1e13;
- //const int mod = 2600000069;
- //const int p = 179;
- int n;
- vector<int> a, t_was, t_inv2;
- void update(vector<int>& t, int v, int l, int r, int pos, int val) {
- if (r - l == 1) {
- t[v] = val;
- return;
- }
- int m = (l + r) / 2;
- if (pos < m) {
- update(t, 2 * v + 1, l, m, pos, val);
- } else {
- update(t, 2 * v + 2, m, r, pos, val);
- }
- t[v] = t[2 * v + 1] + t[2 * v + 2];
- }
- int get_sum(vector<int>& t, int v, int l, int r, int askl) {
- if (r <= askl) {
- return 0;
- }
- if (l >= askl) {
- return t[v];
- }
- int m = (l + r) / 2;
- return get_sum(t, 2 * v + 1, l, m, askl) + get_sum(t, 2 * v + 2, m, r, askl);
- }
- signed main() {
- ios_base::sync_with_stdio(0);
- cin.tie(0);
- cout.tie(0);
- cin >> n;
- a.resize(n);
- t_was.assign(4 * n, 0);
- t_inv2.assign(4 * n, 0);
- for (int i = 0; i < n; i++) {
- cin >> a[i];
- }
- map<int, int> ind;
- vector<int> b = a;
- sort(all(b));
- for (int i = 0; i < n; i++) ind[b[i]] = i;
- int inv2;
- int ans = 0;
- for (int i = 0; i < n; i++) {
- inv2 = get_sum(t_was, 0, 0, n, ind[a[i]] + 1);
- ans += get_sum(t_inv2, 0, 0, n, ind[a[i]] + 1);
- update(t_was, 0, 0, n, ind[a[i]], 1);
- update(t_inv2, 0, 0, n, ind[a[i]], inv2);
- }
- cout << ans;
- }
- /*
- 3
- 3 2 1
- -> 1
- 3
- 2 3 1
- -> 0
- 4
- 10 8 3 1
- -> 4
- 4
- 1 5 4 3
- -> 1
- */
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