111.minimum-depth-of-binary-tree.py

#
# @lc app=leetcode id=111 lang=python3
#
# [111] Minimum Depth of Binary Tree
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# https://leetcode.com/problems/minimum-depth-of-binary-tree/description/
#
# algorithms
# Easy (44.05%)
# Likes:    5329
# Dislikes: 1072
# Total Accepted:    894.2K
# Total Submissions: 2M
# Testcase Example:  '[3,9,20,null,null,15,7]'
#
# 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.
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# Note: A leaf is a node with no children.
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# 
# Example 1:
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# 
# Input: root = [3,9,20,null,null,15,7]
# Output: 2
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# 
# Example 2:
# 
# 
# Input: root = [2,null,3,null,4,null,5,null,6]
# Output: 5
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# 
# 
# Constraints:
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# 
# The number of nodes in the tree is in the range [0, 10^5].
# -1000 <= Node.val <= 1000
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# 
#

# @lc code=start
# 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: Optional[TreeNode]) -> int:
        if not root:
            return 0
        queue = [root]
        depth = 1
        while len(queue) > 0:
            size = len(queue)
            for _ in range(size):
                cur = queue.pop(0)
                if not cur.left and not cur.right:
                    return depth
                if cur.left:
                    queue.append(cur.left)
                if cur.right:
                    queue.append(cur.right)
            depth += 1
        return depth
        
# @lc code=end