66 lines
1.8 KiB
Ruby
66 lines
1.8 KiB
Ruby
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require_relative '../../Data-Structures/Ruby/tree_node'
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# Given a binary tree, return its largest internal binary search tree.
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# @param {TreeNode} root
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# @return {TreeNode.val[]}
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def largest_internal_binary_search_tree(root)
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binary_search_trees = []
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nodes_to_visit = [root]
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while nodes_to_visit.count > 0
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current_root = nodes_to_visit.pop
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current_tree, additional_nodes_to_visit = current_binary_search_tree(current_root)
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binary_search_trees << current_tree unless current_tree.count == 1
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nodes_to_visit += additional_nodes_to_visit
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end
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binary_search_trees.max_by(&:count)
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end
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# @param {TreeNode} root
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# @return {[TreeNode[], TreeNode[]]}
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def current_binary_search_tree(root)
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current_tree = []
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unvisited_nodes = [] # Nodes to call current_binary_search_tree on from largest_internal_binary_search_tree
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valid_children = []
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loop do
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if valid_node? root
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current_tree << root
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if valid_node? root.left
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valid_children << root.left
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elsif !root.left.nil?
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unvisited_nodes << root.left
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end
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if valid_node? root.right
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valid_children << root.right
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elsif !root.right.nil?
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unvisited_nodes << root.right
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end
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break if valid_children.count == 0
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root = valid_children.shift
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else
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unvisited_nodes << root.left unless root.left.nil?
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unvisited_nodes << root.right unless root.right.nil?
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break
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end
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end
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[current_tree, unvisited_nodes]
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end
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def valid_node?(node)
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# The binary search tree property states that the key in each node must be greater than all
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# keys stored in the left sub-tree, and smaller than all keys in right sub-tree.
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if !node || (node.left && node.data <= node.left.data) || (node.right && node.data >= node.right.data)
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false
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else
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true
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end
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end
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