Submission #1285022

#	Time	Username	Problem	Language	Result	Execution time	Memory
1285022		jackofall718	Mountains (NOI20_mountains)	C++20	100 / 100	350 ms	33316 KiB

Mountains

#include <bits/stdc++.h>
#include <chrono>
#define ll long long int
#define endl '\n'
#define vn vector<ll>
#define vi vector<pair <ll,ll>>

using namespace std;
using namespace std::chrono;
const ll INF = 0x3f3f3f3f3f3f3f;

#define pb push_back  
#define srt(vp) sort(vp.begin(), vp.end()) 
#define pii pair<ll,ll>

struct fenwick{
    vn bit;
    ll n;
    fenwick(ll size){
        n=size;
        bit.assign(n+1,0);


    }

    void update(ll i, ll val){
        for (;i<=n; i+= i & -i){//; at the start
            bit[i]+= val;

        }
    }
    
    ll query(ll i){
        ll sum = 0;
        for (;i>0; i-= i&-i){// > not >= cuz 1-based
            sum += bit[i];
        }
        return sum;
    }



};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    auto start = high_resolution_clock::now();

    ll n;
    cin >> n;
    vn v(n);
    for (int i = 0; i < n; i++) cin >> v[i];

    vn arr = v;
    sort(arr.begin(),arr.end());
    arr.erase(unique(arr.begin(),arr.end()),arr.end());
    map <ll,ll> pos;
    for (int i=0;i<arr.size();i++){
        pos[arr[i]]=i+1;

    }
    for (int i=0;i<n;i++){
        v[i]=pos[v[i]];
    }
    ll size = arr.size();
    vn left(n,0);
    vn right(n,0);
    fenwick bitL(size);
    fenwick bitR(size);

    for (int i=0;i<n;i++){
        left[i]=bitL.query(v[i]-1);
        bitL.update(v[i],1);
    }
    for (int i=n-1;i>=0;i--){
        right[i]=bitR.query(v[i]-1);
        bitR.update(v[i],1);
    }
    ll ans = 0;
    for (int i=0;i<n;i++){
        ans += left[i]*right[i];


    }
    cout<<ans<<endl;




     

    

    

    auto stop = high_resolution_clock::now();
    auto duration = duration_cast<microseconds>(stop - start);
    // cout << "Time taken by function: " << duration.count() << " microseconds" << endl;

    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