111. Minimum Depth of Binary Tree

Problem Link

Description

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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

Solution

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Python3

# 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
        
        q = collections.deque([[root,1]])
        
        while q:
            node, level = q.popleft()
            
            if node:
                if not node.left and not node.right:
                    return level
                
                for n in (node.left,node.right):
                    if n:
                        q.append([n, level + 1])