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.
Note: A leaf is a node with no children.
Example:
Given binary tree [3,9,20,null,null,15,7]
,
3
/ \
9 20
/ \
15 7
return its minimum depth = 2.
LeetCode:链接
和LeetCode104:Maximum Depth of Binary Tree要区分出来。
如果根节点为空,那么返回0,如果左子树为空,返回右子树的最低高度+1,右子树为空,返回左子树最低高度+1,否则返回min(左子树最低高度,右子树最低高度)+1。
# 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 root == None:
return 0
if not root.left:
return 1 + self.minDepth(root.right)
elif not root.right:
return 1 + self.minDepth(root.left)
else:
return 1 + min(self.minDepth(root.left), self.minDepth(root.right))