题目描述：
LeetCode 662. Maximum Width of Binary Tree
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.
题目大意：
给定二叉树，求二叉树的最大宽度。二叉树某层的宽度是指其最左非空节点与最右非空节点之间的跨度。
解题思路：
二叉树层次遍历
对二叉树节点进行标号，根节点标号为1；若某节点标号为c，则其左右孩子标号分别为2c, 2c + 1
某层的宽度即为最右、最左节点标号之差+1
Python代码：
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def widthOfBinaryTree(self, root):
"""
:type root: TreeNode
:rtype: int
"""
q = [(root, 1)]
ans = 0
while q:
width = q[-1][-1] - q[0][-1] + 1
ans = max(ans, width)
q0 = []
for n, i in q:
if n.left: q0.append((n.left, i * 2))
if n.right: q0.append((n.right, i * 2 + 1))
q = q0
return ans
本文链接：http://bookshadow.com/weblog/2017/08/21/leetcode-maximum-width-of-binary-tree/
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