Leetcode Problem 1008. Construct Binary Search Tree from Preorder Traversal

1008. Construct Binary Search Tree from Preorder Traversal

Leetcode Solutions

Initialize the current index idx to 0, which will track the position in the preorder list.
Define a recursive helper function helper(lower, upper) that will construct the BST: a. If idx is equal to the length of the preorder list, return None as the tree is constructed. b. Get the current value val from the preorder list using idx. c. If val is not within the lower and upper limits, return None. d. Increment idx to move to the next element in the preorder list. e. Create a new tree node with the value val. f. Recursively call helper(lower, val) to construct the left subtree. g. Recursively call helper(val, upper) to construct the right subtree. h. Return the constructed tree node.
Call helper(float('-inf'), float('inf')) to start the recursion with the initial limits and construct the BST.
Return the root of the constructed BST.

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