11 lines of Python DFS solution

  • 1
    def countUnivalSubtrees(root):
        def dfs(root):
            if root == None:
                return True
            l, r = dfs(root.left), dfs(root.right)
            lval = root.left.val if root.left else root.val
            rval = root.right.val if root.right else root.val
            prev, cnt[0] = cnt[0], cnt[0] + (root.val == lval == rval and l and r)
            return prev != cnt[0]
        cnt = [0]
        return cnt[0]

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