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# Definition for a binary tree node.
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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 isUnivalTree(self, root: Optional[TreeNode]) -> bool:
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        val1 = root.val
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        self.tracker = False
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        def dfs(root, val1):
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            if not root:
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                return
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            if root.val != val1:
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                self.tracker = True
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            dfs(root.left, val1)
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            dfs(root.right, val1)
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            return
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        dfs(root, val1)
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        if self.tracker == False:
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            return True
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        return False