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Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a full binary tree, but some nodes are null.
The width of one level is defined as the length between the end-nodes (the leftmost and right most non-null nodes in the level, where the null nodes between the end-nodes are also counted into the length calculation.
Example 1:
Input:
1
/ \
3 2
/ \ \
5 3 9
Output: 4
Explanation: The maximum width existing in the third level with the length 4 (5,3,null,9).
Example 2:
Input:
1
/
3
/ \
5 3
Output: 2
Explanation: The maximum width existing in the third level with the length 2 (5,3).
Example 3:
Input:
1
/ \
3 2
/
5
Output: 2
Explanation: The maximum width existing in the second level with the length 2 (3,2).
Example 4:
Input:
1
/ \
3 2
/ \
5 9
/ \
6 7
Output: 8
Explanation:The maximum width existing in the fourth level with the length 8 (6,null,null,null,null,null,null,7).
Note: Answer will in the range of 32-bit signed integer.
原始的BFS都是习惯Q从后面pop，这里要维持左右顺序，所以要用deque从左边pop
# Definition for a binary tree node.
class Solution(object):
def widthOfBinaryTree(self, root):
"""
:type root: TreeNode
:rtype: int
"""
from collections import deque
if not root: return 0
q,qq=deque([root]),deque()
res=1
while q:
while q:
t=q.popleft()
qq.append(t.left if t else None)
qq.append(t.right if t else None)
q,qq=qq,q
while q and not q[0]: q.popleft()
while q and not q[-1]: q.pop()
res=max(res,len(q))
return res