Submission #1286128

#	Time	Username	Problem	Language	Result	Execution time	Memory
1286128		samarthkulkarni	Mountains (NOI20_mountains)	C++20	100 / 100	751 ms	99716 KiB

Mountains

#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;

// #pragma GCC target ("avx2")
// #pragma GCC optimize ("O3")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC optimize("fast-math")

#define ll long long
#define ld long double
#define vi vector<ll>
#define endl "\n"
#define pr pair<ll, ll>
#define ff first 
#define ss second
#define all(x) x.begin(), x.end()
const int mod = 1e9+7;
void _p(ll a){cout<<a<<endl;}
void _p(string a){cout<<a<<endl;}
void _p(ld a) {cout<<a<<endl;}
template <class T>
void _p(vector<T> a){for(T val:a)cout<<val<<" ";cout<<endl;}
#define debug(x) cout<<#x<<" -> ";_p(x)

typedef tree<ll, null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update > ordered_set;

vector<pr> move8 = {{1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}, {0, -1}, {1, -1}};
vector<pr> move4 = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
vector<pr> move2 = {{0, 1}, {1, 0}};



void solution();
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    solution();
    return 0;
}
	
struct Node {
	vi x;
	Node* left;
	Node* right;
	Node() {left = nullptr; right = nullptr;}
};

struct WaveletTree{	
	ll n;
	vi a;
	vi idx;
	Node* root;
	WaveletTree(const vi &temp, ll mx) {
		n = mx;
		a = temp;
		idx.resize(a.size());
		iota(all(idx), 0);
		root = new Node();
	}

	Node* build(ll l, ll r, vi &curr) {
		Node* m = new Node();
		m->x = curr;
		if (l == r) {
			return m;
		}

		ll mid = (l + r)/2;
		vi L, R; 
		for (auto val : curr) {
			if (a[val] <= mid) L.push_back(val);
			else R.push_back(val);
		}

		m->left = build(l, mid, L);
		m->right = build(mid+1, r, R);
		return m;
	}

	ll binarySearch(vi& temp, ll l, ll r) {
		return upper_bound(all(temp), r) - upper_bound(all(temp), l-1);
	}

	ll query(Node* curr, ll l, ll r, ll L, ll R, ll c, ll d) {
		if (R < L) return 0;
		if (c > r || l > d) return 0;
		if (c <= l && d >= r) return binarySearch(curr->x, L, R);

		ll mid = (l + r)/2;
		ll a1 = query(curr->left, l, mid, L, R, c, d);
		ll a2 = query(curr->right, mid+1, r, L, R, c, d);
		return  a1 + a2;
	}

	void build() {root = build(0, n, idx);}
	ll query(ll l, ll r, ll c, ll d) {return query(root, 0, n, l, r, c, d);}
};

void solution() {
    ll n; cin >> n;
    vi a(n);
    for (ll &z : a) cin >> z;

    vi temp(a);
	sort(all(temp));
	temp.erase(unique(all(temp)), temp.end());
	for (int i = 0; i < n; i++) a[i] = lower_bound(all(temp), a[i]) - temp.begin();

    WaveletTree M(a, *max_element(all(a)));
	M.build();


	ll ans = 0;


	for (int i = 1; i < n-1; i++) {
		ans += M.query(0, i-1, 0, a[i]-1) * M.query(i+1, n, 0, a[i]-1);
	}

	cout << ans << endl;


}

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12