首发于 语雀文档@blueju

    代码：

    1. /**
    2.  * Definition for a binary tree node.
    3.  * class TreeNode {
    4.  *     val: number
    5.  *     left: TreeNode | null
    6.  *     right: TreeNode | null
    7.  *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
    8.  *         this.val = (val===undefined ? 0 : val)
    9.  *         this.left = (left===undefined ? null : left)
    10.  *         this.right = (right===undefined ? null : right)
    11.  *     }
    12.  * }
    13.  */
    15. function buildTree(inorder: number[], postorder: number[]): TreeNode | null {
    16.     if (inorder.length === 0 || inorder.length === 0)
    17.         return null
    19.     const rootValue = postorder.slice(-1)[0]
    20.     const tree = new TreeNode(rootValue)
    22.     const rootIndex = inorder.findIndex(item => item === rootValue)
    23.     const leftInorder = inorder.slice(0, rootIndex)
    24.     const rightInorder = inorder.slice(rootIndex + 1)
    26.     tree.left = buildTree(leftInorder, postorder.slice(0, leftInorder.length))
    27.     tree.right = buildTree(rightInorder, postorder.slice(leftInorder.length, -1))
    28.     return tree
    29. };