第一道算法题 ``` function t10(arr) { const arr1 = [] arr.forEach(item => { arr1.push({id: item.id, children: []}) }) for (let i = arr.length-1; i >=0; i--) { if (arr[i].parentId!==null){ let item=arr1.pop() arr1[arr[i].parentId-1].children.push(item) } } return arr1 } ```