#341

Flatten Nested List Iterator

specialist · 660 · lc medium +30 · 65.6% accepted · 5,068 likes · top 70%

Description

You are given a nested list of integers nestedList where each element is either an integer or a further-nested list. Construct a flattening iterator that yields integers in the natural left-to-right traversal order.

Implement the NestedIterator class:

- NestedIterator(List<NestedInteger> nestedList) Sets up the iterator over nestedList.

- int next() Advances past and returns the next integer.

- boolean hasNext() Returns true when at least one integer remains.

Validation pseudocode:

initialize iterator with nestedList
res = []
while iterator.hasNext()
append iterator.next() to the end of res
return res

Your iterator passes if res matches the fully flattened list.

Example 1:

initialize iterator with nestedList

res = []

while iterator.hasNext()

append iterator.next() to the end of res

return res

Example 2:

Input: nestedList = [[1,1],2,[1,1]]

Output: [1,1,2,1,1]

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

Example 3:

Input: nestedList = [1,[4,[6]]]

Output: [1,4,6]

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

Code

# """
# 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]):
        
    
    def next(self) -> int:
        
    
    def hasNext(self) -> bool:
         

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

# """
# 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]):
        
    
    def next(self) -> int:
        
    
    def hasNext(self) -> bool:
         

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