
ZOJ Problem Set  3185
A list is a sequence of zero or more elements, expressed in this form: [a_{1}, a_{2}, a_{3}, ... , a_{n}], where each a_{i} is one or more consecutive digits or lowercase letters. i.e. each list begins with a left square bracket, then zero or more elements separated by a single comma, followed by a right square bracket. There will be no whitespace characters (spaces, TABs etc) within a list. In this problem, we use two list operations: append (++) and remove (). 1. A ++ B: append elements in B to the end of A. 2. A  B: remove all the elements in B, from A. If something appears more than once in B, remove it that many times in A. If there are many equal elements in A to choose from, remove them from left to right (until all occurrences are removed, or there is no need to remove more elements). Your task is to write a calculator, evaluating simple expressions or the form "list1 ++ list2" or "list1  list2". Input There will be at most 10 expressions, one in each line, each having the form "list1 ++ list2" or "list1  list2", with no more than 80 characters in total (not counting the newline character). There will be exactly two spaces in each line: one before and one after the operator. Input ends with a single dot. The input is guaranteed to satisfy the restrictions stated above. Output For each expression, print its result on a single line. Sample Input [1,2,3] ++ [1,2,3] [a,b,c,t,d,e,t,x,y,t]  [t] [a,b,c,t,d,e,t,x,y,t]  [t,t,t,t] [123] ++ [456] . Sample Output [1,2,3,1,2,3] [a,b,c,d,e,t,x,y,t] [a,b,c,d,e,x,y] [123,456] Author: LIU, Rujia Source: The 34th ACMICPC Asia Regional 2009 Ningbo Site NIT Cup National Invitation Contest 