111. Minimum Depth of Binary Tree

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 1:

Input: root = [3,9,20,null,null,15,7]
Output: 2

Example 2:

Input: root = [2,null,3,null,4,null,5,null,6]
Output: 5

def minDepth(self, root: Optional[TreeNode]) -> int:
	if not root:
		return 0
	if not root.left:
		return 1 + self.minDepth(root.right)
	if not root.right:
		return 1 + self.minDepth(root.left)
	return 1 + min(self.minDepth(root.left), self.minDepth(root.right))