【leetcode】Minimum Depth of Binary Tree

題目簡述：

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.

解題思路：

# 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
    # @return an integer
    min = 99999
    def minDeep(self, root, cur):
        if root == None:
            self.min = 0
            return 
        cur += 1
        if root.left == None and root.right ==None:
            if self.min >cur:
                self.min = cur
                return
        
        if root.left != None:
            self.minDeep(root.left, cur)
        if root.right != None:
            self.minDeep(root.right, cur)
        
    def minDepth(self, root):
        self.minDeep(root, 0)
        return self.min