2021年10月4日（105. 从前序与中序遍历序列构造二叉树）

首发于 语雀文档@blueju

代码：

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */
function buildTree(preorder, inorder) {
    if (preorder.length === 0 || inorder.length === 0) return null
    const root = preorder[0]
    const rootInInorderIndex = inorder.findIndex(item => item === root)
    const left = inorder.slice(0, rootInInorderIndex)
    const right = inorder.slice(rootInInorderIndex + 1)
    const tree = new TreeNode(root)
    tree.left = buildTree(preorder.slice(1, left.length + 1), left)
    tree.right = buildTree(preorder.slice(left.length + 1), right)
    return tree
};