111.二叉树的最小深度.py

#
# @lc app=leetcode.cn id=111 lang=python
#
# [111] 二叉树的最小深度
#
# https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/description/
#
# algorithms
# Easy (40.38%)
# Likes:    165
# Dislikes: 0
# Total Accepted:    34.2K
# Total Submissions: 84.8K
# Testcase Example:  '[3,9,20,null,null,15,7]'
#
# 给定一个二叉树，找出其最小深度。
# 
# 最小深度是从根节点到最近叶子节点的最短路径上的节点数量。
# 
# 说明: 叶子节点是指没有子节点的节点。
# 
# 示例:
# 
# 给定二叉树 [3,9,20,null,null,15,7],
# 
# ⁠   3
# ⁠  / \
# ⁠ 9  20
# ⁠   /  \
# ⁠  15   7
# 
# 返回它的最小深度  2.
# 
#

# @lc code=start
# 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 minDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:return 0
        
        if not root.left:return self.minDepth(root.right)+1
        if not root.right:return self.minDepth(root.left)+1

        return min(self.minDepth(root.left),self.minDepth(root.right))+1
        # @lc code=end