You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.
Implement the NestedIterator class:
-
NestedIterator(List<NestedInteger> nestedList)Initializes the iterator with the nested listnestedList. -
int next()Returns the next integer in the nested list. -
boolean hasNext()Returnstrueif there are still some integers in the nested list andfalseotherwise.
Your code will be tested with the following pseudocode:
initialize iterator with nestedList
res = []
while iterator.hasNext()
append iterator.next() to the end of res
return res
If res matches the expected flattened list, then your code will be judged as correct.
Example 1:
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 2:
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].
Constraints:
-
1 <= nestedList.length <= 500 - The values of the integers in the nested list is in the range
[-106, 106].
SOLUTION:
# """
# 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.arr = []
self.expand(nestedList)
self.i = 0
def expand(self, nestedList):
for nl in nestedList:
if nl.isInteger():
self.arr += [nl.getInteger()]
else:
self.expand(nl.getList())
def next(self) -> int:
self.i += 1
return self.arr[self.i - 1]
def hasNext(self) -> bool:
return self.i < len(self.arr)
# Your NestedIterator object will be instantiated and called as such:
# i, v = NestedIterator(nestedList), []
# while i.hasNext(): v.append(i.next())
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