class MyQueue: def __init__(self): self.stack_in = [] self.stack_out = [] def push(self, x): self.stack_in.append(x) def pop(self): if not self.stack_out: while self.stack_in: self.stack_out.append(self.stack_in.pop()) return self.stack_out.pop() def peek(self): if not self.stack_out: while self.stack_in: self.stack_out.append(self.stack_in.pop()) return self.stack_out[-1] def empty(self): return not self.stack_in and not self.stack_out