1008. Construct Binary Search Tree from Preorder Traversal

Return the root node of a binary search tree that matches the given preorder traversal.

(Recall that a binary search tree is a binary tree where for every node, any descendant of node.left has a value < node.val, and any descendant of node.right has a value > node.val. Also recall that a preorder traversal displays the value of the node first, then traverses node.left, then traverses node.right.)

It's guaranteed that for the given test cases there is always possible to find a binary search tree with the given requirements.

Example 1:

Input: [8,5,1,7,10,12]
Output: [8,5,10,1,7,null,12]
![](https://assets.leetcode.com/uploads/2019/03/06/1266.png)

Constraints:

• 1 <= preorder.length <= 100
• 1 <= preorder[i] <= 10^8
• The values of preorder are distinct.

# @lc code=start
using LeetCode

function bst_from_preorder(preorder::AbstractVector{Int})
    if isempty(preorder)
        return nothing
    end
    i, f = 2, preorder[1]
    root = TreeNode(f)
    while i <= length(preorder) && preorder[i] < f
        i += 1
    end
    i -= 1
    root.left = bst_from_preorder(@view preorder[2:i])
    root.right = bst_from_preorder(@view preorder[(i + 1):end])
    return root
end
# @lc code=end

bst_from_preorder (generic function with 1 method)

This page was generated using DemoCards.jl and Literate.jl.