| 1 | # implement a queue using two stacks |
| 2 | |
| 3 | class Stack(): |
| 4 | def __init__(self): |
| 5 | self.list=[] |
| 6 | |
| 7 | def __len__(self): |
| 8 | return len(self.list) |
| 9 | |
| 10 | def push(self,item): |
| 11 | self.list.append(item) |
| 12 | |
| 13 | def pop(self): |
| 14 | if len(self.list)==0: |
| 15 | return None |
| 16 | return self.list.po() |
| 17 | |
| 18 | class QueueviaStack(): |
| 19 | def __init__(self): |