341_FlattenNestedListIterator.py

# coding: utf8


"""
    题目链接: https://leetcode.com/problems/flatten-nested-list-iterator/description.
    题目描述:

    Given a nested list of integers, implement an iterator to flatten it.

    Each element is either an integer, or a list -- whose elements may also be integers or other lists.

    Example 1:
    Given the list [[1,1],2,[1,1]],

    By calling next repeatedly until hasNext returns false, the order of elements returned by next should be:
    [1,1,2,1,1].

    Example 2:
    Given the list [1,[4,[6]]],

    By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

"""


# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
# class NestedInteger(object):
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """

class NestedIterator(object):

    def __init__(self, nestedList):
        """
        Initialize your data structure here.
        :type nestedList: List[NestedInteger]
        """
        self.stack = []
        for n in nestedList[::-1]:
            self.stack.append(n)

    def next(self):
        """
        :rtype: int
        """
        return self.stack.pop()

    def hasNext(self):
        """
        :rtype: bool
        """
        while self.stack:
            # 内嵌列表, 出栈, 继续平铺展开
            # 直至栈顶为整数
            while self.stack and not self.stack[-1].isInteger():
                s = self.stack.pop().getList()
                for i in s[::-1]:
                    self.stack.append(i)

            if self.stack and self.stack[-1].isInteger():
                return True

        return False

# Your NestedIterator object will be instantiated and called as such:
# i, v = NestedIterator(nestedList), []
# while i.hasNext(): v.append(i.next())