Construct Binary Tree from Preorder and Inorder Traversal

[cheatsheet1999]

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

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This is a very basic question and tested us about inorder and preorder traverse.

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {number[]} preorder
 * @param {number[]} inorder
 * @return {TreeNode}
 */
var buildTree = function(preorder, inorder) {
    if(!inorder.length) return null;
   // The first node of preorder is always the root of the tree
    let root = new TreeNode(preorder.shift())
    let index = inorder.indexOf(root.val);
   // Inorder traverse, every elements on the left side of the root would be the left tree,
   // the elements on the right of the root will be the right subtree
    let leftTree = inorder.slice(0, index);
    let rightTree = inorder.slice(index + 1);
    
    root.left = buildTree(preorder, leftTree);
    root.right = buildTree(preorder, rightTree);
    return root;
};