Submission #8035011

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Source Code Expand

#include <bits/stdc++.h>

//#pragma GCC optimize ("O3")
//#pragma GCC optimize ("Ofast")

#define F first
#define S second
#define MT make_tuple
#define SZ(a) ((int)(a).size())
#define PB push_back
#define LBS 20
#define MOD ((long long)1e9+7) //1e9+9
#define LEFT(i) (2*(i))
#define RIGHT(i) (2*(i)+1)
#define PAR(i) ((i)/2)
#define ALL(a) (a).begin(), (a).end()

using namespace std;

typedef long long ll;
typedef double rat;
typedef long long bi;
typedef pair<int, int> ii;
typedef std::vector<ii> vii;
typedef std::map<int, int> mii;
typedef bitset<LBS> bis;
typedef std::vector<bis> vbs;

template<class T>
void in(T &a){
  for(auto &x: a)
    cin >> x;
}

template<class T>
void out(T &a, string sep=" "){
  for(auto x: a)
    cout << x<<sep;
  cout << '\n';
}

template<class T>
void err(T &a, string sep=" "){
  for(auto x: a)
    cerr << x <<sep;
  cerr << '\n';
}


int main(){
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n; cin >> n;
  std::vector<int> l(n); in(l);
  sort(ALL(l));
  int cc=0;
  for(int i=0; i<n; i++)
    for(int j=i+1; j<n; j++){
      int a=lower_bound(ALL(l),l[i]+l[j])-l.begin();
      int b=upper_bound(ALL(l), abs(l[i]-l[j]))-l.begin();
      cc+=a-b;
      if(b<=i)
        cc--;
      if(b<=j)
        cc--;
      // cerr << i << " "<<j<<" "<<cc<<"\n";
    }
  cout << cc/3 << "\n";
}

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