Question 4.[5 MARKS ] This question deals with lists and stacks. Consider the operation of evaluating postfix expressions. For example, the expression 1233+11 equals 12+3311=34, the expression 1023+ evaluates to 10+23=16. Consider a method with the following signature: public int postfix(List list 1 ) // Precondition: list1 is a linked list containing a postfix expression // example: [12]-> [33]->[+]->[11]->[-] // where each element of the list is either an integer // or an arithmetic operator. // you may assume the epxression is well formed and contains no brackets. // Postconditions: returns the integer value of the expression Part (a) [4 MARKS] Describe an algorithm for implementing this method (in either Java, or pseudocode). Give a brief description of the methods of List class you will use. Hint: use a helper Stack variable. Part (b) [1 MARK] What is the Big-O complexity of your algorithm