从前序与中序遍历序列构造二叉树

给定两个整数数组 preorder 和 inorder 其中 preorder 是二叉树的先序遍历 inorder 是同一棵树的中序遍历请构造二叉树并返回其根节点。/** * Definition for a binary tree node. * function TreeNode(val, left, right) { * this.val (valundefined ? 0 : val) * this.left (leftundefined ? null : left) * this.right (rightundefined ? null : right) * } *//** * param {number[]} preorder * param {number[]} inorder * return {TreeNode} */varbuildTreefunction(preorder,inorder){if(!preorder.length){returnnull;}constcurrentpreorder[0];constrootnewTreeNode(current);constindexinorder.indexOf(current);root.leftbuildTree(preorder.slice(1,index1),inorder.slice(0,index));root.rightbuildTree(preorder.slice(index1),inorder.slice(index1));returnroot;};