1 def quchong(S):
 2         str1=[""]
 3         for i in S:
 4             if i == str1[-1]:
 5                 str1.pop()
 6             else:
 7                 str1.append(i)
 8         print(''.join(str1))
 9 quchong("daaba")
10 quchong("bbaca")
1 dba
2 aca