LeetCode刷题笔记19-5-7

232.用栈实现队列

使用栈实现队列的下列操作：

push(x) – 将一个元素放入队列的尾部。
pop()– 从队列首部移除元素。
peek() – 返回队列首部的元素。
empty() – 返回队列是否为空。
示例:

MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
queue.peek(); // 返回 1
queue.pop(); // 返回 1
queue.empty(); // 返回 false

class MyQueue:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.InStack=[] #分别设置两个栈
        self.OutStack=[]

    def push(self, x: int) -> None:
        """
        Push element x to the back of queue.
        """
        self.InStack.append(x)

    def pop(self) -> int:
        """
        Removes the element from in front of queue and returns that element.
        """
        if self.OutStack==[]:    #注意只有当出栈为空时，才进行trans！！！
            self.trans()
        return self.OutStack.pop(-1)
        
    def trans(self):
        while(self.InStack!=[]):
            rear=self.InStack.pop(-1)
            self.OutStack.append(rear)

    def peek(self) -> int:
        """
        Get the front element.
        """
        if self.OutStack==[]:
            self.trans()
        return self.OutStack[-1]

    def empty(self) -> bool:
        """
        Returns whether the queue is empty.
        """
        if self.OutStack==[] and self.InStack==[]:
            return True
        return False


# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()

用队列实现栈

直接贴上代码吧！

class MyStack:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.InQueue=[]
        self.TempQueue=[]  #建立一个临时储存的栈

    def push(self, x: int) -> None:
        """
        Push element x onto stack.
        """
        self.InQueue.append(x)
        
        
    def pop(self) -> int:
        """
        Removes the element on top of the stack and returns that element.
        """
        self.trans()
        top=self.InQueue.pop(0)  #原始栈出栈只剩1个元素后，复制临时栈到新的原始栈
        self.InQueue=self.TempQueue
        self.TempQueue=[]
        return top
        
    def trans(self):
        while(len(self.InQueue)!=1):
            front=self.InQueue.pop(0)
            self.TempQueue.append(front)

    def top(self) -> int:
        """
        Get the top element.
        """
        self.trans()
        top=self.InQueue[0]
        self.TempQueue.append(top)
        self.InQueue=self.TempQueue
        self.TempQueue=[]
        return top

    def empty(self) -> bool:
        """
        Returns whether the stack is empty.
        """
        if self.InQueue==[]:
            return True
        return False


# Your MyStack object will be instantiated and called as such:
# obj = MyStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()