[leetcode]Minimum Depth of Binary Tree @ Python

原題地址：http://oj.leetcode.com/problems/minimum-depth-of-binary-tree/

題意：

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：分幾種情況考慮：1，樹為空，則為0。 2，根節點如果只存在左子樹或者只存在右子樹，則返回值應為左子樹或者右子樹的（最小深度+1）。 3，如果根節點的左子樹和右子樹都存在，則返回值為（左右子樹的最小深度的較小值+1）。

代碼：

# 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
    def minDepth(self, root):
        if root == None:
            return 0
        if root.left == None and root.right != None:
            return self.minDepth( root.right ) + 1
        if root.left != None and root.right == None:
            return self.minDepth( root.left ) + 1
        return min( self.minDepth( root.left ), self.minDepth( root.right ) ) + 1