leetcode第106题 从中序与后序遍历序列构造二叉树

题目： 给定两个整数数组 inorder 和 postorder ，其中 inorder 是二叉树的中序遍历， postorder 是同一棵树的后序遍历，请你构造并返回这颗 二叉树 。 题目链接

我的JavaScript解法

/**
 * 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}
 */
var buildTree = function(inorder, postorder) {
  return build(postorder, 0, postorder.length - 1, inorder, 0, inorder.length -1);
};
const build = (postorder, posStart, posEnd, inorder, inStart, inEnd) => {
  if (inStart > inEnd) return null;
  const rootValue = postorder[posEnd];
  const rootIndex = inorder.indexOf(rootValue);
  const leftTreeSize = rootIndex - inStart;
  const root = new TreeNode(rootValue);
  root.left = build(postorder, posStart, posStart + leftTreeSize - 1, inorder, inStart, rootIndex - 1);
  root.right = build(postorder, posStart + leftTreeSize, posEnd - 1, inorder, rootIndex + 1, inEnd);
  return root;
};