Language: C++

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;

class hawawa
{
  static Printer sw = new Printer(Console.OpenStandardOutput()) { AutoFlush = false };

  static void Main()
  {
    Console.SetOut(sw);
    solve();
    Console.Out.Flush();
  }

  static string target;

  static void solve()
  {
    Scanner scanner = new Scanner();
    target = scanner.next();
    Console.WriteLine(dfs(target) ? "Yes" : "No");
  }

  static bool dfs(string str)
  {
    if (set.Contains(str)) return false;
    if (str == "ABC") return true;
    set.Add(str);
    int size = str.Count();
    for (char c = 'A'; c <= 'C'; c++)
    {
      int num = size - str.Replace(c.ToString(), "").Count();
      if (size - str.Replace("ABC", "").Count() == num * 3 && dfs(str.Replace("ABC", c.ToString())))
      {
        return true;
      }
    }
    return false;
  }
  static List<string> set = new List<string>();

}

class Scanner
{
  string[] s;
  int i;


  char[] cs = new char[] { ' ' };

  public Scanner()
  {
    s = new string[0];
    i = 0;
  }

  public string next()
  {
    if (i < s.Length) return s[i++];
    string st = Console.ReadLine();
    while (st == "") st = Console.ReadLine();
    s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
    i = 0;
    return next();
  }

  public int nextInt()
  {
    return int.Parse(next());
  }

  public long nextLong()
  {
    return long.Parse(next());
  }

  public double nextDouble()
  {
    return double.Parse(next());
  }

}


class Printer : StreamWriter
{
  public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
  public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
  public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { }
}



Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Globalization;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.IO;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Linq;
      |       ^~~~~~
a.cc:6:7: error: expected nested-name-specifier before 'System'
    6 | using System.Text;
      |       ^~~~~~
a.cc:10:10: error: 'Printer' does not name a type
   10 |   static Printer sw = new Printer(Console.OpenStandardOutput()) { AutoFlush = false };
      |          ^~~~~~~
a.cc:19:10: error: 'string' does not name a type
   19 |   static string target;
      |          ^~~~~~
a.cc:28:19: error: 'string' has not been declared
   28 |   static bool dfs(string str)
      |                   ^~~~~~
a.cc:44:10: error: 'List' does not name a type
   44 |   static List<string> set = new List<string>();
      |          ^~~~
a.cc:46:2: error: expected ';' after class definition
   46 | }
      |  ^
      |  ;
a.cc: In static member function 'static void hawawa::Main()':
a.cc:14:5: error: 'Console' was not declared in this scope
   14 |     Console.SetOut(sw);
      |     ^~~~~~~
a.cc:14:20: error: 'sw' was not declared in this scope
   14 |     Console.SetOut(sw);
      |                    ^~
a.cc: In static member function 'static void hawawa::solve()':
a.cc:23:5: error: 'Scanner' was not declared in this scope
   23 |     Scanner scanner = new Scanner();
      |     ^~~~~~~
a.cc:24:5: error: 'target' was not declared in this scope
   24 |     target = scanner.next();
      |     ^~~~~~
a.cc:24:14: error: 'scanner' was not declared in this scope
   24 |     target = scanner.next();
      |              ^~~~~~~
a.cc:25:5: error: 'Console' was not declared in this scope
   25 |     Console.WriteLine(dfs(target) ? "Yes" : "No");
      |     ^~~~~~~
a.cc: In static member function 'static bool hawawa::dfs(int)':
a.cc:30:9: error: 'set' was not declared in this scope
   30 |     if (set.Contains(str)) return false;
      |         ^~~
a.cc:31:13: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   31 |     if (str == "ABC") return true;
      |         ~~~~^~~~~~~~
a.cc:32:5: error: 'set' was not declared in this scope
   32 |     set.Add(str);
      |     ^~~
a.cc:33:20: error: request for member 'Count' in 'str', which is of non-class type 'int'
   33 |     int size = str.Count();
      |                    ^~~~~
a.cc:36:28: error: request for member 'Replace' in 'str', which is of non-class type 'int'
   36 |       int num = size - str.Replace(c.ToString(), "").Count();
      |                            ^~~~~~~
a.cc:36:38: error: request for member 'ToString' in 'c', which is of non-class type 'char'
   36 |       int num = size - str.Replace(c.ToString(), "").Count();
      |                                      ^~~~~~~~
a.cc:37:22: error: request for member 'Replace' in 'str', which is of non-class type 'int'
   37 |       if (size - str.Replace("ABC", "").Count() == num * 3 && dfs(str.Replace("ABC", c.ToString())))
      |                      ^~~~~~~
a.cc:37:71: error: request for member 'Replace' in 'str', which is of non-class type 'int'
   37 |       if (size - str.Replace("ABC", "").Count() == num * 3 && dfs(str.Replace("ABC", c.ToString())))
      |                                                                       ^~~~~~~
a.cc:37:88: error: request for member 'ToString' in 'c', which is of non-class type 'char'
   37 |       if (size - str.Replace("ABC", "").Count() == num * 3 && dfs(str.Replace("ABC", c.ToString())))
      |                                                                                        ^~~~~~~~
a.cc: At global scope:
a.cc:50:3: error: 'string' does not name a type
   50 |   string[] s;
      |   ^~~~~~
a.cc:54:7: error: expected unqualified-id before '[' token
   54 |   char[] cs = new char[] { ' ' };
      |       ^
a.cc:56:9: error: expected ':' before 'Scanner'
   56 |   public Scanner()
      |         ^~~~~~~~
      |         :
a.cc:62:9: error: expected ':' before 'string'
   62 |   public string next()
      |         ^~~~~~~
      |         :
a.cc:62:10: error: 'string' does not name a type
   62 |   public string next()
      |          ^~~~~~
a.cc:72:9: error: expected ':' before 'int'
   72 |   public int nextInt()
      |         ^~~~
      |         :
a.cc:77:9: error: expected ':' before 'long'
   77 |   public long nextLong()
      |         ^~~~~
      |         :
a.cc:82:9: error: expected ':' before 'double'
   82 |   public double nextDouble()
      |         ^~~~~~~
      |         :
a.cc:87:2: error: expected ';' after class definition
   87 | }
      |  ^
      |  ;
a.cc: In constructor 'Scanner::Scanner()':
a.cc:58:5: error: 's' was not declared in this scope
   58 |     s = new string[0];
      |     ^
a.cc:58:13: error: 'string' does not name a type
   58 |     s = new string[0];
      |             ^~~~~~
a.cc: In member function 'int Scanner::nextInt()':
a.cc:74:12: error: expected primary-expression before 'int'
   74 |     return int.Parse(next());
      |            ^~~
a.cc:74:12: error: expected ';' before 'int'
a.cc:74:15: error: expected unqualified-id before '.' token
   74 |     return int.Parse(next());
      |               ^
a.cc: In member function 'long int Scanner::nextLong()':
a.cc:79:12: error: expected primary-expression before 'long'
   79 |     return long.Parse(next());
      |            ^~~~
a.cc:79:12: error: expected ';' before 'long'
a.cc:79:16: error: expected unqualified-id before '.' token
   79 |     return long.Parse(next());
      |                ^
a.cc: In member function 'double Scanner::nextDouble()':
a.cc:84:12: error: expected primary-expression before 'double'
   84 |     return double.Parse(next());
      |            ^~~~~~
a.cc:84:12: error: expected ';' before 'double'
a.cc:84:18: error: expected unqualified-id before '.' token
   84 |     return double.Parse(next());
      |                  ^
a.cc: At global scope:
a.cc:91:1: error: expected class-name before '{' token
   91 | {
      | ^
a.cc:92:9: error: expected ':' before 'override'
   92 |   public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
      |         ^~~~~~~~~
      |         :
a.cc:92:10: error: 'override' does not name a type
   92 |   public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
      |          ^~~~~~~~
a.cc:93:9: error: expected ':' before 'Printer'
   93 |   public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
      |         ^~~~~~~~
      |         :
a.cc:93:24: error: expected ')' before 'stream'
   93 |   public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
      |                 ~      ^~~~~~~
      |                        )
a.cc:94:9: error: expected ':' before 'Printer'
   94 |   public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { }
      |         ^~~~~~~~
      |         :
a.cc:94:24: error: expected ')' before 'stream'
   94 |   public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { }
      |                 ~      ^~~~~~~
      |                        )
a.cc:95:2: error: expected ';' after class definition
   95 | }
      |  ^
      |  ;