Construct Binary Tree from Inorder and Postorder Traversal

Problem statement

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

Example 1:

Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]Output: [3,9,20,null,null,15,7]

Example 2:

Input: inorder = [-1], postorder = [-1]Output: [-1]

Constraints:

• 1 <= inorder.length <= 3000
• postorder.length == inorder.length
• -3000 <= inorder[i], postorder[i] <= 3000
• inorder and postorder consist of unique values.
• Each value of postorder also appears in inorder.
• inorder is guaranteed to be the inorder traversal of the tree.
• postorder is guaranteed to be the postorder traversal of the tree.

My solution

/**
 * 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[]} inorder
 * @param {number[]} postorder
 * @return {TreeNode}
 */
const map = new Map()
var buildTree = function(inorder, postorder) {
    const len = inorder.length
    for (let i = 0; i < inorder.length; i++) {
        map.set(inorder[i], i)
    }
    const root = traverse(inorder, postorder, 0, len - 1, 0, len - 1)
    return root
};

function traverse(inOrder, postOrder, inOrderStart, inOrderEnd, postOrderStart, postOrderEnd) {
    if (inOrderStart > inOrderEnd) {
        return null
    }
    
    const node = new TreeNode(postOrder[postOrderEnd])
    
    if (inOrderStart === inOrderEnd) {
        return node;
    }
    
    const idx = map.get(node.val);
    
    node.left = traverse(inOrder, postOrder, inOrderStart, idx - 1, postOrderStart, postOrderStart - inOrderStart + idx - 1)
    
    node.right = traverse(inOrder, postOrder, idx + 1, inOrderEnd, postOrderEnd - inOrderEnd + idx, postOrderEnd - 1)
    
    return node
}

function search(inOrder, left, right, target) {
    let i;
    for (i = left; i <= right; i++) {
        if (inOrder[i] === target) {
            return i
        }
    }
    return i;
}