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  1. Hello! How can I help you?
  2.  
  3. Can you write me code to validate whether a list of binary tree nodes forms exactly one valid tree.
  4.  
  5. Sure, here's an example code in Python to validate if a list of binary tree nodes forms exactly one valid tree:
  6.  
  7. class TreeNode:
  8. def __init__(self, val):
  9. self.val = val
  10. self.left = None
  11. self.right = None
  12.  
  13. def validate_tree(nodes):
  14. # Creating a dictionary with key as the node value and value as the TreeNode object
  15. node_dict = {node['val']: TreeNode(node['val']) for node in nodes}
  16.  
  17. # Iterating through the list of nodes to create the tree structure using parent-child relationships
  18. for node in nodes:
  19. # Getting the node object
  20. parent_node = node_dict[node['val']]
  21. # Getting the left child node object
  22. if node['left'] is not None:
  23. left_child = node_dict[node['left']]
  24. parent_node.left = left_child
  25. # Getting the right child node object
  26. if node['right'] is not None:
  27. right_child = node_dict[node['right']]
  28. parent_node.right = right_child
  29.  
  30. # Counting the number of root nodes
  31. roots = 0
  32. for node in node_dict.values():
  33. if not node.left and not node.right:
  34. roots += 1
  35. elif (node.left and not node.right) or (not node.left and node.right):
  36. return False
  37.  
  38. # Validating that only one root node is present in the tree
  39. return roots == 1
  40. The validate_tree function takes a list of nodes, each node represented as a dictionary with the keys val , left , and right , where val is the node value and left and right are the values of the left and right child nodes respectively.
  41.  
  42. The function first creates a dictionary with the node values as the keys and the corresponding TreeNode objects as the values. It then iterates through the input list of nodes to create the tree structure using parent-child relationships.
  43.  
  44. After the tree structure is created, the function counts the number of root nodes present in the tree. A node is considered to be a root node if it has no children. If a node has only one child or has two children, it cannot be a root node. Finally, the function validates whether there is only one root node present in the tree, and returns True if it is valid, and False otherwise.
  45.  
  46. Note that this function assumes that the input list of nodes represents a valid binary tree, i.e., there are no loops in the tree structure and each node has at most two children.
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