Submission #1369631

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Source Code Expand

#include<iostream>
#include<algorithm>
#include<iomanip>
#include<cmath>
#include<vector>
using namespace std;
int main(){

  int n, a;
  vector<int> r;
  cin >> n;
  
  for(int i=0; i<n; i++){
    cin >> a;
    r.push_back(a);
  }

  sort(r.begin(), r.end());
  reverse(r.begin(), r.end());
  double ans = 0;

  for(int i=n-1; i>=0; i--){
    ans += r[i] * r[i] * pow(-1, i);
  }
  cout << fixed;
  cout << setprecision(7) << fabs(ans * M_PI) << endl;
  return 0;
}

Submission Info

Judge Result