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.
# Definition for a binary tree node.
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution:
def minDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if root is None:
return 0
if root.left is None:
return self.minDepth(root.right) + 1
if root.right is None:
return self.minDepth(root.left) + 1
return 1+min(self.minDepth(root.left),self.minDepth(root.right))