232. 用栈实现队列

代码：

class MyQueue(object):

    def __init__(self):
        self.arr1 = []
        self.arr2 = []

    def push(self, x):
        """
        :type x: int
        :rtype: None
        """
        self.arr1.append(x)

    def pop(self):
        """
        :rtype: int
        """
        if len(self.arr2)>0:
            return self.arr2.pop()
        while len(self.arr1)>0:
            self.arr2.append(self.arr1.pop())
        return self.arr2.pop()
        

    def peek(self):
        """
        :rtype: int
        """
        if len(self.arr2)>0:
            return self.arr2[len(self.arr2)-1]
        while len(self.arr1)>0:
            self.arr2.append(self.arr1.pop())
        return self.arr2[len(self.arr2)-1]

    def empty(self):
        """
        :rtype: bool
        """
        if len(self.arr1)==0 and len(self.arr2)==0:
            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()

225.用队列实现栈

代码：

class MyStack(object):

    def __init__(self):
        self.arr = []
        self.i = -1

    def push(self, x):
        """
        :type x: int
        :rtype: None
        """
        self.arr.append(x)
        self.i+=1


    def pop(self):
        """
        :rtype: int
        """
        while self.i>0:
            self.arr.append(self.arr.pop(0))
            self.i-=1
        t = self.arr.pop(0)
        if len(self.arr)==0:
            self.i=-1
        else:
            self.i = len(self.arr)-1
        return t
        

    def top(self):
        """
        :rtype: int
        """
        return self.arr[self.i]

    def empty(self):
        """
        :rtype: bool
        """
        if len(self.arr)==0:
            return True
        return False

20. 有效的括号

代码：

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        str = list(s)
        stack = []
        for i in str:
            if len(stack)==0:
                stack.append(i)
            else:
                if i==')' and stack[len(stack)-1]== '(':
                    stack.pop()
                elif i== '}'and stack[len(stack)-1]=='{':
                    stack.pop()
                elif i== ']'and stack[len(stack)-1]=='[':
                    stack.pop()
                else:
                    stack.append(i)
        if len(stack)==0:
            return True
        return False

1047. 删除字符串中的所有相邻重复项

代码：

class Solution(object):
    def removeDuplicates(self, s):
        """
        :type s: str
        :rtype: str
        """
        my_list = []
        is_delete=True
        str = list(s)
        while is_delete:
            is_delete=False
            for i in str:
                if len(my_list)==0:
                    my_list.append(i)
                else:
                    if i==my_list[len(my_list)-1]:
                        my_list.pop()
                        is_delete=True
                        continue
                    else:
                        my_list.append(i)
            str = my_list
            my_list=[]
        return ''.join(str)