剑指 Offer 09. 用两个栈实现队列
Difficulty: 简单
用两个栈实现一个队列。队列的声明如下,请实现它的两个函数 appendTail
和 deleteHead
,分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素,deleteHead
操作返回 -1 )
示例 1:
输入:
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出:[null,null,3,-1]
示例 2:
输入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出:[null,-1,null,null,5,2]
提示:
1 <= values <= 10000
最多会对 appendTail、deleteHead 进行 10000 次调用
Solution
两个栈,一个入栈一个出栈,新的元素直接入inStack,实现先进先出的效果则需要把元素从inStack中逐个弹出并压入outStack中,这样最后入栈的元素就位于outStack的底部了,最先入栈的元素在顶部。
class CQueue:
def __init__(self):
self.inStack = []
self.outStack = []
def appendTail(self, value: int) -> None:
return self.inStack.append(value)
def deleteHead(self) -> int:
if not self.outStack:
while self.inStack:
self.outStack.append(self.inStack.pop())
if self.outStack:
return self.outStack.pop()
else:
return -1
# Your CQueue object will be instantiated and called as such:
# obj = CQueue()
# obj.appendTail(value)
# param_2 = obj.deleteHead()