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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define FAST ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  4. typedef long long ll;
  5.  
  6.  
  7. vector<ll> lucky_nums;
  8. void generate_lucky(ll number){
  9.  
  10.     lucky_nums.push_back(number);
  11.  
  12.     if(number > 1e10) return;
  13.  
  14.     generate_lucky((number * 10) + 4);
  15.     generate_lucky((number * 10) + 7);
  16. };
  17.  
  18.  
  19. int main() {
  20.     FAST
  21.     ll n;
  22.     cin >>n;
  23.     int fours,sevens;
  24.     generate_lucky(0);
  25.     vector<ll> result;
  26.     lucky_nums.erase(lucky_nums.begin());
  27.     for(auto c : lucky_nums){
  28.         string check = to_string(c);
  29.         fours = 0;
  30.         sevens = 0;
  31.         for(int i = 0;i<check.length();i++){
  32.             if(check[i]=='4'){
  33.                 fours++;   
  34.             }
  35.             else {
  36.                 sevens++;
  37.             }
  38.         }
  39.         if (fours==sevens && (sevens!=0||fours!=0)){
  40.             result.push_back(c);
  41.         }
  42.  
  43.     }
  44.     sort(result.begin(),result.end());
  45.  
  46.     cout << *lower_bound(result.begin(),result.end(),n) << "\n";
  47.  
  48.     // system("pause");
  49.     return 0;
  50. }
Success #stdin #stdout 0.01s 5316KB
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https://ideone.com/2Ds8Ec
language:
C++14 (gcc 8.3)
created:
2 hours ago
visibility:
public

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