flatten-nested-list-iterator.py

# Leetcode 341. Flatten Nested List Iterator
#
# Link: https://leetcode.com/problems/flatten-nested-list-iterator/
# Difficulty: Medium

# Solution using queue (deque based)
# Complexity:
#   O(N) time | where N represent the number of elements in the input list
#   O(N) space | where N represent the number of elements in the input list

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

class NestedIterator:
    def __init__(self, nestedList: [NestedInteger]):

        self.q = deque()

        def flatten(inputList):
            for element in inputList:
                if element.isInteger():
                    self.q.append(element.getInteger())
                else:
                    flatten(element.getList())

        flatten(nestedList)

    def next(self) -> int:
        return self.q.popleft()

    def hasNext(self) -> bool:
        return self.q


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