title: Lexicographically Next String
signature: function lexicographically_next_string(s)
test_code: using Printf
  
  # SOLUTION CODE
  # ============================================
  PLACEHOLDER_CODE_BODY
  
  # TESTING CODE 
  # ============================================
  function validate_solution(actual, expected)
      return actual == expected
  end
  
  function driver(s, expected)
      try
  
          if validate_solution(PLACEHOLDER_FN_NAME(s), expected)
              return "PASSED";
          end
          return "FAILED";
      catch exception_obj
          return string(Base.typename(typeof(exception_obj)).wrapper);
      end
  end
  
  function main()
      
      result = driver("amKIRzPiqLTIy", "amKIRzPiqLTIz");
      @printf("TEST-0...%s\n",result);
      
      result = driver("68", "69");
      @printf("TEST-1...%s\n",result);
      
      result = driver("100", "110");
      @printf("TEST-2...%s\n",result);
      
      result = driver("f", "g");
      @printf("TEST-3...%s\n",result);
      
      result = driver("802205375", "802206375");
      @printf("TEST-4...%s\n",result);
      
      result = driver("0111", "0211");
      @printf("TEST-5...%s\n",result);
      
      result = driver("GRjRYIvYwgua", "GRjRYIvYwgub");
      @printf("TEST-6...%s\n",result);
      
      result = driver("8139910006809", "813:910006809");
      @printf("TEST-7...%s\n",result);
      
      result = driver("100101", "200101");
      @printf("TEST-8...%s\n",result);
      
      result = driver("rw", "rx");
      @printf("TEST-9...%s\n",result);
      
  end
  
  main()
source_py: def lexicographically_next_string(s):
      if (s == ' '):
          return 'a'
      i = (len(s) - 1)
      while ((s[i] == 'z') and (i >= 0)):
          i -= 1
      if (i == (- 1)):
          s = (s + 'a')
      else:
          s = s.replace(s[i], chr((ord(s[i]) + 1)), 1)
      return s
source_cpp: string lexicographically_next_string(string s) {
    if ( s == "" ) return "a";
    int i = s . length ( ) - 1;
    while ( s [ i ] == 'z' && i >= 0 ) i --;
    if ( i == - 1 ) s = s + 'a';
    else s [ i ] ++;
    return s;
  }