Submission #874853

#	Time	Username	Problem	Language	Result	Execution time	Memory
874853		12345678	Mountains (NOI20_mountains)	C++17	100 / 100	170 ms	19400 KiB

Mountains

#include <bits/stdc++.h>

using namespace std;

#define ll long long

const int nx=3e5+5;
ll n, h[nx], t, dp[nx], res;
vector<ll> v;

struct fenwick
{
    ll d[nx];
    void add(int idx)
    {
        for (int i=idx; i<nx; i+=(i&-i)) d[i]++;
    }
    ll query(int idx)
    {
        ll res=0;
        for (int i=idx; i>0; i-=(i&-i)) res+=d[i];
        return res;
    }
} l, r;

int main()
{
    cin.tie(NULL)->sync_with_stdio(false);
    cin>>n;
    for (int i=1; i<=n; i++) cin>>h[i], v.push_back(h[i]);
    sort(v.begin(), v.end());
    for (int i=1; i<=n; i++)
    {
        int idx=lower_bound(v.begin(), v.end(), h[i])-v.begin()+1;
        dp[i]=l.query(idx-1);
        l.add(idx);
    }
    for (int i=n; i>=1; i--)
    {
        int idx=lower_bound(v.begin(), v.end(), h[i])-v.begin()+1;
        res+=dp[i]*r.query(idx-1);
        r.add(idx);
    }
    cout<<res;
}

• 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