Submission #570216

#	Time	Username	Problem	Language	Result	Execution time	Memory
570216		thatsgonzalez	Mountains (NOI20_mountains)	C++14	100 / 100	125 ms	12116 KiB

Mountains

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

typedef long long ll;
typedef vector<ll> vl;
typedef pair <ll,ll> pl;
typedef vector<pl> vpl;

#define s second
#define f first

int n;

struct FT
{
    int n; vl dp;
    FT (int n){
        this->n = n;
        dp.assign(n+1,0);
    }

    int lsb(int x){
        return x & (-x);
    }

    ll query(int ind){
        ll res=0;
        while(ind){
            res+=dp[ind];
            ind-=lsb(ind);
        }
        return res;
    }
    
    void add(int ind, ll value){
        while(ind<=n){
            dp[ind]+=value;
            ind+=lsb(ind);
        }
    }
};

int main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin>>n;
    FT ft1(n),ft2(n);
    ll a[n]; 
    vpl aux(n);
    for(int i=0; i<n; i++){
      ll x; cin>>x; aux[i]={x,i};
    }
    sort(aux.begin(),aux.end()); a[aux[0].s]=1; int temp=1;
    for(int i=1; i<n; i++){
      if(aux[i].f==aux[i-1].f) a[aux[i].s]=temp;
      else temp++, a[aux[i].s]=temp;
    }
    //for(auto &x: a) cout<<x<<" "; cout<<endl; 
    ll mx=0;
    for(int i=n-1; i>=0; i--){
      mx=max(mx,a[i]);
      ft1.add(a[i],1);
    }
    //cout<<query(mx-1,1)<<endl;
    //int top=n+99;
    ll ans=0;
    for(int i=0; i<n; i++){
      ft1.add(a[i],-1LL);
      //cout<<query(a[i]-1,0)<<" "<<query(a[i]-1,1)<<endl;
      ans+=(ll)(ft1.query(a[i]-1)*(ft2.query(a[i]-1)));
      ft2.add(a[i],1LL);
    }
    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