leetcode 111 二叉树的最小深度
z
 2019-07-02 10:10:41  

给定一个二叉树，找出其最小深度。

最小深度是从根节点到最近叶子节点的最短路径上的节点数量。

说明: 叶子节点是指没有子节点的节点。

示例:

给定二叉树 [3,9,20,null,null,15,7],

3

/
9 20
/
15 7
返回它的最小深度 2.

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def minDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        def getDepth(root, level):
            if not root:
                return
            if not root.left and not root.right:
                depth.append(level+1) 
            getDepth(root.left, level+1)
            getDepth(root.right, level+1)
            
        depth = []
        getDepth(root, 0)
        return 0 if not depth else min(depth)
    
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class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        left = self.minDepth(root.left)
        right = self.minDepth(root.right)
        if not left:
            return right + 1
        if not right:
            return left + 1
        return min(left, right) + 1
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from collections import deque

class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        q, depth = deque(), 1
        q.append((root, depth))
        while q:
            node, depth = q.popleft()
            if not node:
                continue
            if not node.left and not node.right:
                break
            q.append((node.left, depth+1))
            q.append((node.right, depth+1))
        return depth