title: Minimum Number Of Bracket Reversals Needed To Make An Expression Balanced
signature: function minimum_number_of_bracket_reversals_needed_to_make_an_expression_balanced(expr)
test_code: 
  
  -- SOLUTION CODE
  -- ============================================
  PLACEHOLDER_CODE_BODY
  
  -- TESTING CODE 
  -- ============================================
  function isCorrect(actual, expected)
      if type(expected) ~= type(actual) then
          return false
      end
      
      if type(expected) == 'table' then
          for k,v_expected in pairs(expected) do
              
              if actual[k] == nil then
                  return false
              end
              local v_actual = actual[k]
              if not isCorrect(v_actual, v_expected) then
                  return false
              end
              actual[k]=nil
          end
      
          if next(actual) then 
              return false
          end
          return true
      else
          return actual == expected
      end
  end
  
  function validateSolution(actual, expected)
      return isCorrect(actual,expected)
  end
  
  function driver(expr, expected)
      local exec_result;
      local status, error_msg = pcall(function () 
          exec_result=PLACEHOLDER_FN_NAME(expr) 
      end)
      if status then
          if validateSolution(exec_result,expected) then
              return "PASSED"
          end
          return "FAILED"
      else
          return string.format("ERROR=%s",string.gsub(error_msg,".*:[%d]+: ",""))
      end
  end
      
  function main()
      result = driver("}{", 1)
      print(string.format("TEST-0...%s",result))
  
      result = driver("{{{", -1)
      print(string.format("TEST-1...%s",result))
  
      result = driver("{{{{", 2)
      print(string.format("TEST-2...%s",result))
  
      result = driver("{{{{}}", 3)
      print(string.format("TEST-3...%s",result))
  
      result = driver("}{{}}{{{", 4)
      print(string.format("TEST-4...%s",result))
  
      result = driver("{}", 1)
      print(string.format("TEST-5...%s",result))
  
      result = driver("", 0)
      print(string.format("TEST-6...%s",result))
  
      result = driver("8", -1)
      print(string.format("TEST-7...%s",result))
  
      result = driver("01111000", 4)
      print(string.format("TEST-8...%s",result))
  
      result = driver("XPkERzHcpId", -1)
      print(string.format("TEST-9...%s",result))
  
  end
  
  main()
source_py: def minimum_number_of_bracket_reversals_needed_to_make_an_expression_balanced(expr):
      lenn = len(expr)
      if (lenn % 2):
          return (- 1)
      s = []
      for i in range(lenn):
          if ((expr[i] == '') and len(s)):
              if (s[0] == ''):
                  s.pop(0)
              else:
                  s.insert(0, expr[i])
          else:
              s.insert(0, expr[i])
      red_len = len(s)
      n = 0
      while (len(s) and (s[0] == '')):
          s.pop(0)
          n += 1
      return ((red_len // 2) + (n % 2))
source_cpp: int minimum_number_of_bracket_reversals_needed_to_make_an_expression_balanced(string expr) {
    int len = expr . length ( );
    if ( len % 2 ) return - 1;
    stack < char > s;
    for ( int i = 0;
    i < len;
    i ++ ) {
      if ( expr [ i ] == '}' && ! s . empty ( ) ) {
        if ( s . top ( ) == '{' ) s . pop ( );
        else s . push ( expr [ i ] );
      }
      else s . push ( expr [ i ] );
    }
    int red_len = s . size ( );
    int n = 0;
    while ( ! s . empty ( ) && s . top ( ) == '{' ) {
      s . pop ( );
      n ++;
    }
    return ( red_len / 2 + n % 2 );
  }