"""
111. Minimum Depth of Binary Tree
Easy

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, 105].
    -1000 <= Node.val <= 1000

"""
# 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
from collections import deque
class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        q = deque([(root, 1)])
        while q:
            n, lvl = q.popleft()
            if not n.left and not n.right:
                return lvl
            if n.left:
                q.append((n.left, lvl+1))
            if n.right:
                q.append((n.right, lvl+1))
