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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define int long long
  5.  
  6. const int MaxN = (int)1e6 + 5;
  7. const int MOD = (int)1e9 + 7;
  8.  
  9. int n;
  10. int s[MaxN];
  11. int cnt[MaxN];
  12. int ans;
  13.  
  14. signed main(){
  15.     ios::sync_with_stdio(0);
  16.     cin.tie(0);
  17.     cin >> n;
  18.     for(int i = 1; i <= n; i++){
  19.         cin >> s[i];
  20.         cnt[s[i]]++;
  21.     }
  22.     sort(s + 1, s + 1 + n, greater<int>());
  23.     for(int i = 1; i <= n; i++){
  24.         if(s[i] == 4 && cnt[4] >= 1){
  25.             ++ans;
  26.             cnt[4]--;
  27.         }
  28.         else if(s[i] == 3 && cnt[1] >= 1 && cnt[3] >= 1){
  29.             ++ans;
  30.             cnt[3]--;
  31.             cnt[1]--;
  32.         }
  33.         else if(s[i] == 3 && cnt[1] == 0 && cnt[3] >= 1){
  34.             ++ans;
  35.             cnt[3]--;
  36.         }
  37.         else if(s[i] == 2 && cnt[2] >= 2){
  38.             ++ans;
  39.             cnt[2] -= 2;
  40.         }
  41.         else if((s[i] == 2 && cnt[1] >= 2 && cnt[2] >= 1)){
  42.             ++ans;
  43.             cnt[2]--;
  44.             cnt[1] -= 2;
  45.         }
  46.         else if(s[i] == 2 && cnt[1] >= 1 && cnt[2] >= 1){
  47.             ++ans;
  48.             --cnt[2]; --cnt[1];
  49.         }
  50.         else if(s[i] == 2 && cnt[2] >= 1 && cnt[1] == 0){
  51.             ++ans;
  52.             cnt[2]--;
  53.         }
  54.         else if(s[i] == 1 && cnt[1] >= 1){
  55.             int b = 1;
  56.             while(b <= 4 && cnt[1] > 0){
  57.                 --cnt[1];
  58.                 ++b;
  59.             }
  60.             ++ans;
  61.         }
  62.     }
  63.     cout << ans;
  64.     return 0;
  65. }
  66.  
Success #stdin #stdout 0s 5296KB
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https://ideone.com/XT2Kpb
language:
C++14 (gcc 8.3)
created:
2 days ago
visibility:
public

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