问题描述
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].
问题分析
运用栈的思想，当栈为空时，从NestedList头部拿一个元素到stack；
当stack的栈顶元素不为Integer，则取栈顶原素，将其列表成员按逆序加入栈；
需要注意的一点是，其实取next的主要工作是在hasNext做的，因为只有得到了next整数，才能证明有next，而取next只要取栈顶元素即可。还需要注意，NestedList可能是有空数组，例如“[[]]”。
AC代码
# """
# 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 = []
self.nested = nestedList
def next(self):
"""
:rtype: int
"""
return self.stack.pop().getInteger()
def hasNext(self):
"""
:rtype: bool
"""
while self.stack or self.nested:
if not self.stack:
self.stack.append(self.nested.pop(0))
while self.stack and not self.stack[-1].isInteger():
tmp = self.stack.pop().getList()
for t in tmp[::-1]:
self.stack.append(t)
if self.stack:
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())
