fork download
copy 
  1. #include "bits/stdc++.h"
  2.  
  3. #define ll long long int
  4. #define vll vector<ll>
  5. #define vi vector<int>
  6. #define pll pair<long long, long long>
  7. #define vpll vector < pair<long long,long long> >
  8. #define all(c) c.begin(),c.end()
  9. #define pb push_back
  10. #define nl cout << '\n'
  11. #define ff first
  12. #define ss second
  13. #define mod 998244353
  14. #define inf 1000000000000000001
  15.  
  16. #define rep(i, n)      for(int i = 0; i <  n; ++i)
  17. #define repA(i, a, n)  for(int i = a; i <= n; ++i)
  18. #define repD(i, a, n)  for(int i = a; i >= n; --i)
  19.  
  20. using namespace std;
  21.  
  22. void solve(){
  23.     ll n, m, h;
  24.     cin >> n >> m >> h;
  25.     vll v(m);
  26.     rep(i, m){
  27.         cin >> v[i];
  28.     }
  29.  
  30.     ll tot = 0;
  31.     for(auto i: v)
  32.         tot += i;
  33.     if (tot < n)
  34.     {
  35.         cout << -1;
  36.         return;
  37.     }
  38.     if (v[h] == 1 or n == 1)
  39.     {
  40.     	cout << 0;
  41.     	return;
  42.     }
  43.     cout << fixed << setprecision(20) << (n-1) / (double)(tot - 1);
  44. }
  45.  
  46. int main(){
  47.     // ios::sync_with_stdio(0);
  48.     // cin.tie(0); cout.tie(0);
  49.  
  50.     int t = 1, tmp = 0;
  51.     // cin >> t;
  52.     while(t--){
  53.         // cout << "Case #" << ++tmp << ": ";
  54.         solve();
  55.         if(t) cout << "\n";
  56.     }
  57.     cerr << "Time : " << (double)clock() / (double)CLOCKS_PER_SEC << "s\n";
  58.     return 0;
  59. }
Success #stdin #stdout #stderr 0s 5284KB
comments (?)
stdin
copy 
3 2 1
2 2
stdout
copy 
0.66666666666666662966
stderr
copy 
Time : 0.004456s
https://ideone.com/qJvDgX
language:
C++14 (gcc 8.3)
created:
90 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!