算法-数据结构-栈与列表

算法

1. 有效的括号

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class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack=[]
        kuo_hao={"(":")","{":"}","[":"]"}
        for a in s:
            if a in kuo_hao:
                stack.append(a)
            else:
                if not stack:
                    return False
                if stack and kuo_hao[stack.pop()]!=a:
                    return False
        return not stack

2. 两个队列实现一个栈

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# 存使用l ,取也是l只不过是最后一个。
class MyStack(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.queue_l=[]
        self.queue_r=[]
        
        
    def push(self, x):
        """
        Push element x onto stack.
        :type x: int
        :rtype: None
        """
        self.queue_l.append(x)
        

    def pop(self):
        """
        Removes the element on top of the stack and returns that element.
        :rtype: int
        """
        while len(self.queue_l)>1:
            self.queue_r.append(self.queue_l.pop(0))
        value= self.queue_l.pop(0)
        while self.queue_r:
            self.queue_l.append(self.queue_r.pop(0))
        return value
        

    def top(self):
        """
        Get the top element.
        :rtype: int
        """
        while len(self.queue_l)>1:
            self.queue_r.append(self.queue_l.pop(0))
        value= self.queue_l.pop(0)
        if value is not None:
            self.queue_r.append(value)
        while self.queue_r:
            self.queue_l.append(self.queue_r.pop(0))
        return value
        

    def empty(self):
        """
        Returns whether the stack is empty.
        :rtype: bool
        """
        return not self.queue_l

3. 两个栈实现一个队列

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# 存放在l,取从r中取，再把r中值晴空写回l
class MyQueue(object):

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

    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: None
        """
        self.stack_l.append(x)

    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        while self.stack_l:
            self.stack_r.append(self.stack_l.pop())
        value= self.stack_r.pop()
        while self.stack_r:
            self.stack_l.append(self.stack_r.pop())
        return value

    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        while self.stack_l:
            self.stack_r.append(self.stack_l.pop())
        value= self.stack_r.pop()
        self.stack_r.append(value)
        while self.stack_r:
            self.stack_l.append(self.stack_r.pop())
        return value

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        while self.stack_l:
            self.stack_r.append(self.stack_l.pop())
        return (not self.stack_r)