Submission #1087902

#	Time	Username	Problem	Language	Result	Execution time	Memory
1087902		vuavisao	Mountains (NOI20_mountains)	C++14	100 / 100	121 ms	7064 KiB

Mountains

#include <bits/stdc++.h>
using namespace std;

const int N = (int) 3e5 + 10;

int n;
long long a[N];

int L[N], R[N];
int tree[N];

void Update(int idx, int val) {
	for( ; idx <= n; idx += (idx & - idx)) tree[idx] += val;
}

int Query(int idx) {
	int res = 0;
	for( ; idx > 0; idx -= (idx & - idx)) res += tree[idx];
	return res;
}

void compress() {
	vector<long long> Pos = {};
	for (int i = 1; i <= n; ++ i) {
		Pos.push_back(a[i]);
	}
	
	sort(Pos.begin(), Pos.end());
	Pos.resize(unique(Pos.begin(), Pos.end()) - Pos.begin());

	for (int i = 1; i <= n; ++ i) {
		a[i] = lower_bound(Pos.begin(), Pos.end(), a[i]) - Pos.begin() + 1;
	}
}

void calc(int cnt[]) {
	for (int i = 0; i <= n; ++ i) tree[i] = 0;
	for (int i = 1; i <= n; ++ i) {
		cnt[i] = Query(a[i]);
		Update(a[i] + 1, 1);
	}
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr); cout.tie(nullptr);
	cin >> n;
	for (int i = 1; i <= n; ++ i) cin >> a[i];
	compress();
	calc(L);
	reverse(a + 1, a + 1 + n);
	calc(R);
	long long res = 0;
	for (int i = 1; i <= n; ++ i) res += 1ll * L[i] * R[n - i + 1];
	cout << res;
	return 0;
}

• 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