comefrom: <awangdev>844. Backspace String Compare_2.java
code: private String build(String s) {
  
          Stack<Character> stack = new Stack<>();
          for (char c : s.toCharArray()) {
              if (c != '#') stack.push(c);
              else if (!stack.isEmpty()) stack.pop();
          }
          StringBuffer sb = new StringBuffer();
          while (!stack.isEmpty()) sb.insert(0, stack.pop());
          return sb.toString();
      }
masked: private String var_0 ( String var_2 ) {
    Stack < Character > var_5 = new Stack < > ( ) ;
    for ( char var_7 : var_2 . toCharArray ( ) ) {
      if ( var_7 != '#' ) var_5 . push ( var_7 ) ;
      else if ( ! var_5 . isEmpty ( ) ) var_5 . pop ( ) ;
    }
    StringBuffer var_13 = new StringBuffer ( ) ;
    while ( ! var_5 . isEmpty ( ) ) var_13 . insert ( 0 , var_5 . pop ( ) ) ;
    return var_13 . toString ( ) ;
  }
  