## 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.

## 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
``````

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