[LeetCode] Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

题目大概意思是说求二叉树的最小深度，

5
/ \
4   8
/   / \
11  13  4
/  \      \
7    2      1

比如这个二叉树的最小深度为3，其实感觉二叉树的很多问题都是用递归方法解决的，这道也不例外，但是大多数递归算法都可以借助栈用循环实现，二叉树的循环遍历也要掌握。下面是代码：

# Definition for a  binary tree node
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None

class Solution:
# @param root, a tree node
# @param sum, an integer
# @return a boolean
def minDepth(self, root):
if None == root:
return 0
if None == root.left and None == root.right:
return 1
if None != root.left and None != root.right:
return 1 + min(self.minDepth(root.left), self.minDepth(root.right))
elif None != root.left:
return 1 + self.minDepth(root.left)
elif None != root.right:
return 1 + self.minDepth(root.right)