展平包含子列表的列表

Question

我想让我的解决方案通过Leetcode的在线评判。问题是：给定一个嵌套的整数列表，实现一个迭代器来展平它。你知道吗

每个元素要么是一个整数，要么是一个列表——其元素也可以是整数或其他列表。你知道吗

例1： 给定列表[[1,1]，2，[1,1]]

通过反复调用next直到hasNext返回false，next返回的元素顺序应该是：[1,1,2,1,1]

完整的问题是here。你知道吗

问题表明它将实例化使用以下代码实现的类：

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

下面是我的解决方案：

class NestedIterator(object):
    currIdx = 0

    def __init__(self, nestedList):
        """
        Initialize your data structure here.
        :type nestedList: List[NestedInteger]
        """
        newFlattenedList = []
        self.flattenList(nestedList, newFlattenedList)
        nestedList = newFlattenedList
        self.flattenedList = nestedList

    def flattenList(self, nestedList, flattenedList):

        for ele in nestedList:
            if type(ele) == list and ele  > 0:
                self.flattenList(ele, flattenedList)
            else:
                flattenedList.append(ele)
        return

    def next(self):
        """
        :rtype: int
        """
        if self.hasNext():

            test = self.flattenedList[self.currIdx]
            self.currIdx +=1
            return test
        else:
            return NULL 

    def hasNext(self):
        """
        :rtype: bool
        """
        nextIdx = self.currIdx + 1 
        return True if nextIdx <= len(self.flattenedList) else False

当我在IDE中用输入[[1,1]，2，[1,1]]运行这段代码时，得到的输出是[1,1,2,1,1]。出于某种原因，当我使用online judge运行代码时，给定输入[[1,1]，2，[1,1]]，输出是[[1,1]，返回2，[1,1]]。为什么leetcode在线评委会返回不同的结果？你知道吗

Answer 1

你的解决方案有两个问题。你知道吗

1. 在下一个方法中将returnnull更改为None。你知道吗
2. 在flattelist中，ele的大小比较只适用于python2！为它添加len（）函数以在python3上工作。你知道吗

这是修改后的代码。应该到处都是。你知道吗

class NestedIterator(object):
    currIdx = 0

    def __init__(self, nestedList):
        """
        Initialize your data structure here.
        :type nestedList: List[NestedInteger]
        """
        newFlattenedList = []
        self.flattenList(nestedList, newFlattenedList)
        nestedList = newFlattenedList
        self.flattenedList = nestedList

    def flattenList(self, nestedList, flattenedList):

        for ele in nestedList:
            if type(ele) == list and len(ele)  > 0:
                self.flattenList(ele, flattenedList)
            else:
                flattenedList.append(ele)
        return

    def next(self):
        """
        :rtype: int
        """
        if self.hasNext():

            test = self.flattenedList[self.currIdx]
            self.currIdx +=1
            return test
        else:
            return None

    def hasNext(self):
        """
        :rtype: bool
        """
        nextIdx = self.currIdx + 1
        return True if nextIdx <= len(self.flattenedList) else False

Answer 2

你是说None不是NULL对吧？你知道吗

def next(self):
    """
    :rtype: int
    """
    if self.hasNext():

        test = self.flattenedList[self.currIdx]
        self.currIdx +=1
        return test
    else:
        #return NULL 
        return None

通过运行：

nestedList = [[1,1],2,[1,1]]
i, v = NestedIterator(nestedList), []
while i.hasNext(): v.append(i.next())

print v

我得到了：

[1, 1, 2, 1, 1]

所以，除了把NULL改成None，我不知道。你知道吗