用栈实现队列

def solve():
    class MyQueue:
        def __init__(____):
            self.in_stack = []
            self.out_stack = []
        
        def push(____):
            self.in_stack.append(____)
        
        def pop(____):
            if not self.out_stack:
                while self.in_stack:
                    self.out_stack.append(self.in_stack.pop())
            return self.out_stack.pop()
    
    q = MyQueue()
    q.push(____)
    q.push(____)
    result = [str(q.pop())]
    q.push(____)
    result.append(str(q.pop()))
    print('____'.join(____))