[leetcode] 341. Flatten Nested List Iterator @ python

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原题

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:

Input: [[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: [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].

解法

双向队列. 我们在初始化的时候就将nestedList转换成deque, 利用题目中定义的方法, 我们遍历nestedList, 如果元素是整数, 那么直接加到deque里, 如果元素是nestedList, 那么递归求解.
next函数就是每次在左边删除一个数字, hasNext函数就是查看deque的长度是否大于0.

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]
        """
        def flatten(nestedList):
            for l in nestedList:
                if l.isInteger():
                    self.q.append(l)
                else:
                    flatten(l.getList())
                    
        self.q = collections.deque()
        flatten(nestedList)        
        

    def next(self):
        """
        :rtype: int
        """
        return self.q.popleft()

    def hasNext(self):
        """
        :rtype: bool
        """
        return len(self.q)> 0

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