Construct Binary Tree from Preorder and Inorder

Given preorder and inorder traversal arrays, construct the binary tree.

Output the level-order traversal of the constructed tree, space-separated.

Input:

3,9,20,15,7
9,3,15,20,7

Output:

3 9 20 null null 15 7

Reasoning:

The preorder traversal array [3, 9, 20, 15, 7] represents the order in which nodes are visited: root, left subtree, right subtree. The first element 3 is the root node.
The inorder traversal array [9, 3, 15, 20, 7] represents the order in which nodes are visited: left subtree, root, right subtree. This helps to identify the left and right child nodes of the root 3, which are 9 and 20 respectively.
The left subtree of 3 only contains 9, and the right subtree of 3 is constructed from the remaining elements [15, 20, 7] in the inorder array, with 20 as the root, 15 as its left child, and 7 as its right child.
The constructed binary tree is then traversed level-by-level to produce the output: 3 (root), 9 (left child of 3), 20 (right child of 3), null (no left child of 9), null (no right child of 9), 15 (left child of 20), 7 (right child of 20).