## Question

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

**Constraints:**

- The number of nodes in the tree is in the range
`[0, 10`

.^{5}] `-1000 <= Node.val <= 1000`

## Python Solution

# Definition for a binary tree node. # class TreeNode: # def __init__(self, val=0, left=None, right=None): # self.val = val # self.left = left # self.right = right def find_min(root,level): global m if not root: return if root.left==None and root.right==None:m = min(m,level+1) find_min(root.left,level+1) find_min(root.right,level+1) class Solution: def minDepth(self, root: TreeNode) -> int: global m m = 2**31-1 if root==None:return 0 find_min(root,0) return m