将扁平数组转化为Tree

arrToTree.js

const arrayToTree  = (items) => {
  let results = [];
  let map = {};

  items.forEach(el => {
    let item = {...el, children: []};
    if (map[item.id]) {
      item.children = map[item.id];
    } else {
      map[item.id] = item.children;
    }

    if (item.pid) {
      if (!map[item.pid]) {
        map[item.pid] = [];
      }
      map[item.pid].push(item);
    } else {
      console.log('item: ', item);
      results.push(item);
    }
  });

  map = null;

  return results;
};


let arr = [
  {id: 1, name: '部门1', pid: 0},
  {id: 2, name: '部门2', pid: 1},
  {id: 3, name: '部门3', pid: 1},
  {id: 4, name: '部门4', pid: 3},
  {id: 5, name: '部门5', pid: 4}
];
console.log(arrayToTree(arr));
// 时间复杂度 O(n)