Helicator

folia.cpp

Dec 9th, 2021
707
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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define int long long
  5. #define vi vector<int>
  6. #define ii pair<int,int>
  7. #define fi first
  8. #define sc second
  9. #define stoi stoll
  10. #define popcnt __builtin_popcount
  11. #define getbit(x, k) ((x >> k) & 1)
  12. #define all(x) (x).begin(),(x).end()
  13. #define FOR(i,j,k) for(int i=j; i<k; i++)
  14. #define look(a) cerr <<#a<<": "<<a<<endl;
  15. #define look2(a,b) cerr <<#a<<": "<<a<<" | "<<#b<<": "<<b<< endl;
  16.  
  17. void solve()
  18. {
  19.     int n;
  20.     cin >> n;
  21.     int a[n+1],b[n+1],c[n+1];
  22.     FOR(i,0,n+1) cin >> a[i];
  23.     if (a[0] > 1){
  24.         cout << -1;
  25.         return;
  26.     }
  27.     c[n] = a[n];
  28.     for (int i = n-1; i >= 0; i--){
  29.         c[i] = c[i+1] + a[i];
  30.     }
  31.     b[0] = 1 - a[0];
  32.     FOR(i,1,n+1){
  33.         if (a[i] > b[i-1]*2){
  34.             cout << -1;
  35.             return;
  36.         }
  37.         b[i] = min(c[i+1],b[i-1]*2 - a[i]);
  38.         //look2(c[i+1],b[i-1]*2 - a[i])
  39.         if (a[i] + b[i] < b[i-1]){
  40.             cout << -1;
  41.             return;
  42.         }
  43.     }
  44.     //FOR(i,0,n+1) look2(a[i],b[i]);
  45.     int s = a[n];
  46.     FOR(i,0,n) s += a[i] + b[i];
  47.     cout << s;
  48. }
  49.  
  50. signed main()
  51. {
  52.     cin.tie(0)->sync_with_stdio(0);
  53.     freopen("in", "r", stdin);
  54.     freopen("out", "w", stdout);
  55.     int T = 1;
  56.     // cin >> T;
  57.     while (T--) {
  58.         solve();
  59.         cout << '\n';
  60.     }
  61.     cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
  62. }
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