1class MyQueue:
2 def __init__(self):
3 self.s1 = []; self.s2 = []
4 def push(self, val): self.s1.append(val)
5 def pop(self):
6 self.peek()
7 return self.s2.pop()
8 def peek(self):
9 if not self.s2:
10 while self.s1: self.s2.append(self.s1.pop())
11 return self.s2[-1]