Submission #770140

#	Time	Username	Problem	Language	Result	Execution time	Memory
770140		LucaLucaM	Mountains (NOI20_mountains)	C++17	100 / 100	235 ms	14116 KiB

Mountains

#include <bits/stdc++.h>

typedef long long ll;

using namespace std;

const int NMAX = 3e5;

int aib[NMAX + 5];

int n;

void update (int pos, const int &val)
{
    for (; pos <= n; pos += pos & -pos)
        aib[pos] += val;
}
int query (int pos)
{
    int ret = 0;
    for (; pos; pos -= pos & -pos)
        ret += aib[pos];
    return ret;
}

ll a[NMAX + 5];
ll b[NMAX + 5];

ll ans[NMAX + 5];

int main()
{
    cin >> n;
    for (int i=1; i<=n; i++)
    {
        cin >> a[i];
        b[i] = a[i];
    }
    sort (b+1, b+n+1);
    for (int i=1; i<=n; i++)
    {
        a[i] = lower_bound(b+1, b+n+1, a[i]) - (b + 1) + 1;
    }
    for (int i=1; i<=n; i++)
    {
        ans[i] = query(a[i] - 1);
        update(a[i], +1);
    }
    memset(aib, 0, sizeof(aib));
    for (int i=n; i>0; i--)
    {
        ans[i] *= query(a[i] - 1);
        update(a[i], +1);
    }
    ll sum = 0;
    for (int i=1; i<=n; i++)
        sum += ans[i];
    cout << sum;
    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