Minimum Depth of Binary Tree

min_depth_binary_tree.py

"""
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.

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
"""
# 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
class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        stack, min_depth = [(1, root)], float('inf')
        while stack:
            depth, tree = stack.pop()
            children = [tree.left, tree.right]
            if not any(children):
                min_depth = min(depth, min_depth)
            for child in children:
                if child:
                    stack.append((depth + 1, child))
        return min_depth