实现 convert 方法，把原始 list 转换成树形结构，要求尽可能降低时间复杂度

以下数据结构中，id 代表部门编号，name 是部门名称，parentId 是父部门编号，为 0 代表一级部门，现在要求实现一个 convert 方法，把原始 list 转换成树形结构，parentId 为多少就挂载在该 id 的属性 children 数组下，结构如下：

// 原始 list 如下

let list =[
    {id:1,name:'部门A',parentId:0},
    {id:2,name:'部门B',parentId:0},
    {id:3,name:'部门C',parentId:1},
    {id:4,name:'部门D',parentId:1},
    {id:5,name:'部门E',parentId:2},
    {id:6,name:'部门F',parentId:3},
    {id:7,name:'部门G',parentId:2},
    {id:8,name:'部门H',parentId:4}
];
const result = convert(list, ...);

// 转换后的结果如下

let result = [
    {
      id: 1,
      name: '部门A',
      parentId: 0,
      children: [
        {
          id: 3,
          name: '部门C',
          parentId: 1,
          children: [
            {
              id: 6,
              name: '部门F',
              parentId: 3
            }, {
              id: 16,
              name: '部门L',
              parentId: 3
            }
          ]
        },
        {
          id: 4,
          name: '部门D',
          parentId: 1,
          children: [
            {
              id: 8,
              name: '部门H',
              parentId: 4
            }
          ]
        }
      ]
    },
  ···
];

实现了两种解法, 明显第二种更简单, 时间复杂度更低

export {}
let list =[
  {id:1,name:'部门A',parentId:0},
  {id:2,name:'部门B',parentId:0},
  {id:3,name:'部门C',parentId:1},
  {id:4,name:'部门D',parentId:1},
  {id:5,name:'部门E',parentId:2},
  {id:6,name:'部门F',parentId:3},
  {id:7,name:'部门G',parentId:2},
  {id:8,name:'部门H',parentId:4}
];

interface Dep {
  id: number,
  name: string,
  parentId: number,
  children?: Array
};

function deepCompose(rawList: Array, comList: Array) {
  const depList = rawList.slice();
  while (depList.length > 0) {
    const node = depList.shift();

    // append child nodes
    const children = comList.filter(d => d.parentId === node.id);
    if (children.length === 0) continue;

    node.children = children;

    deepCompose(children, comList);
  }
}

function composeTree(depList: Dep[]) {
  // first sort by parentId asc
  depList.sort((a, b) => a.parentId - b.parentId);

  // filter head
  const [{ parentId }] = depList;
  let rootDepList = depList.filter(dep => dep.parentId === parentId);
  
  deepCompose(rootDepList, depList);

  return rootDepList;
}

const depTree = composeTree(list);
console.log(`${JSON.stringify(depTree)}`);

export {}

let list =[
  {id:1,name:'部门A',parentId:0},
  {id:2,name:'部门B',parentId:0},
  {id:3,name:'部门C',parentId:1},
  {id:4,name:'部门D',parentId:1},
  {id:5,name:'部门E',parentId:2},
  {id:6,name:'部门F',parentId:3},
  {id:7,name:'部门G',parentId:2},
  {id:8,name:'部门H',parentId:4}
];

interface Dep {
  id: number,
  name: string,
  parentId: number,
  children?: Array
};

function composeTree(depList: Array) {
  const depMap = new Map();
  depList.forEach(d => depMap.set(d.id, d));

  for (const d of depList) {
    const parentId = d.parentId;
    if (depMap.has(parentId)) {
      const parentDep = depMap.get(parentId);
      parentDep.children = parentDep.children || [];
      parentDep.children.push(d);
    }
  }

  // filter head list
  depList.sort((a, b) => a.parentId - b.parentId);
  const [{ parentId }] = depList;
  const rootDepList = depList.filter(dep => dep.parentId === parentId);

  return rootDepList;
}

const res = composeTree(list);
console.log(`${JSON.stringify(res)}`);