python bottom up O(n)

  • 0
    class Solution(object):
        def countUnivalSubtrees(self, root):
            self.count = 0
            def helper(root):
                if not root: return True
                l, r = helper(root.left), helper(root.right)
                if not l or not r or root.left and root.val != root.left.val or root.right and root.val != root.right.val:
                    return False
                self.count += 1
                return True
            return self.count

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