Minimum Distance Between BST Nodes LeetCode solution in Python

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# class TreeNode:
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#     def __init__(self, val=0, left=None, right=None):
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#         self.val = val
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#         self.left = left
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#         self.right = right
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class Solution:
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    def minDiffInBST(self, root: Optional[TreeNode]) -> int:
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        if root is None:
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            return 0
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        temp1=float(inf)
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        from collections import deque
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        a=deque([root])
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        b=[]
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        while a:
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            node=a.popleft()
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            b.append(node.val)
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            if node.left:
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                a.append(node.left)
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            if node.right:
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                a.append(node.right)
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        b.sort()
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        for i in range(0,len(b)-1):
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            if b[i+1]-b[i]