LeetCode 946 Validate Stack Sequences

思想：迴圈判斷進棧序列，當進棧序列的值沒有遇到與出棧序列相同時壓棧，迴圈當棧不為空並且出棧序列的第一個值等於棧頂元素時出棧，出棧指標後移，若棧空則序列正確

class Solution(object):
    def validateStackSequences(self, pushed, popped):
        """
        :type pushed: List[int]
        :type popped: List[int]
        :rtype: bool
        """
        stack=[]
        num=len(pushed)
        p=0
        for x in pushed:
            stack.append(x)
            while stack and (stack[-1]==popped[p]):
                stack.pop()                
                p=p+1
        return not len(stack)