## 题目描述：

LeetCode 671. Second Minimum Node In a Binary Tree

Given a non-empty special binary tree consisting of nodes with the non-negative value, where each node in this tree has exactly `two` or `zero` sub-node. If the node has two sub-nodes, then this node's value is the smaller value among its two sub-nodes.

Given such a binary tree, you need to output the second minimum value in the set made of all the nodes' value in the whole tree.

If no such second minimum value exists, output -1 instead.

Example 1:

```Input:
2
/ \
2   5
/ \
5   7

Output: 5
Explanation: The smallest value is 2, the second smallest value is 5.
```

Example 2:

```Input:
2
/ \
2   2

Output: -1
Explanation: The smallest value is 2, but there isn't any second smallest value.
```

## 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 findSecondMinimumValue(self, root):
"""
:type root: TreeNode
:rtype: int
"""
self.ans = 0x80000000
minVal = root.val
def traverse(root):
if not root: return
if self.ans > root.val > minVal:
self.ans = root.val
traverse(root.left)
traverse(root.right)
traverse(root)
return self.ans if self.ans != 0x80000000 else -1
``````

Pingbacks已关闭。

1. 书影网友 发布于 2017年9月4日 00:23 #

`self.ans = 0x80000000` 是有什么特殊含义吗？为啥选取这个数字作为最大值？

2. 书影网友 发布于 2017年9月4日 17:18 #

[6,2,3] failed

3. 书影网友 发布于 2017年9月6日 17:12 #

Oh I see, 这个test是invalid的