Python Leetcode练习二

225.用队列实现栈

class MyStack:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.list = []
        

    def push(self, x: int) -> None:
        """
        Push element x onto stack.
        """
        self.list.append(x)
        

    def pop(self) -> int:
        """
        Removes the element on top of the stack and returns that element.
        """
        if self.list == None:
            return False
        return self.list.pop()
        

    def top(self) -> int:
        """
        Get the top element.
        """
        return self.list[-1]
        

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


# 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()

队列是先进先出，栈是先进后出，所以只要pop的时候取出队列里的最后一个元素即可，并判断此时队列是否为空。

27.移除元素

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        while val in nums:
            nums.remove(val)
        return len(nums)

循环判断val是否在列表里，存在就删除，返回列表长度。

933.最近的请求次数

class RecentCounter:

    def __init__(self):
        self.list = []

    def ping(self, t: int) -> int:
        self.list.append(t)
        
        while len(self.list) != 0:
            if self.list[0] + 3000 < t:
                self.list.pop(0)
            else:
                break
        return len(self.list)

# Your RecentCounter object will be instantiated and called as such:
# obj = RecentCounter()
# param_1 = obj.ping(t)

利用队列先进先出的特点，移除当次 ping 操作不在允许范围内的时间点，剩下的队列内保存的都是允许范围内的时间点，最后返回队列的长度，即为当前时间点 t 所有允许范围内的 ping 操作次数。