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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.
Example 1
Input: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
Output: [3,9,20,null,null,15,7]
Explanation: The first preorder value, 3, is the root. In inorder, [9] is to its left and [15,20,7] to its right. The next preorder value, 20, is the right subtree's root, with 15 on its left and 7 on its right.
Example 2
Input: preorder = [-1], inorder = [-1]
Output: [-1]
Explanation: Both traversals contain only -1, so the tree is that single node.
Example 3
Input: preorder = [1,2,3], inorder = [3,2,1]
Output: [1,2,null,3]
Explanation: Preorder says 1 is the root. In inorder, 3 and 2 both come before 1, so they are in the left subtree. Preorder then gives 2 as that subtree's root, and 3 comes before 2 in inorder, so 3 is 2's left child.
The first value of preorder is always the root. Find that root inside inorder: everything to its left is the left subtree, everything to its right is the right subtree. Recurse, consuming preorder values in order.
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