题目:数组转换树

神女生涯元是梦，小姑居处本无郎。

扁平数组转换树结构

• 输入

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},
]

• 输出结果

[
    {
        "id": 1,
        "name": "部门1",
        "pid": 0,
        "children": [
            {
                "id": 2,
                "name": "部门2",
                "pid": 1,
                "children": []
            },
            {
                "id": 3,
                "name": "部门3",
                "pid": 1,
                "children": [...]
            }
        ]
    }
]

代码实现

1. 双层循环

function arrChangeTree(arr) {
  let idArr = arr.map((val) => val.id);
  let pidArr = arr.map((val) => val.pid);

  for (let i = 0; i < arr.length; i++) {
    pidArr.includes(arr[i].id) ? (arr[i].children = []) : null;
    for (let j = arr.length - 1; j > i; j--) {
      if (arr[i].id == arr[j].pid) {
        arr[i].children.push(arr[j]);
      }
    }
  }
  return arr.filter((val) => !idArr.includes(val.pid));
}

2. 单层循环

function arrChangeTree(arr) {
  let idArr = arr.map((val) => val.id);

  function getChildren(pid) {
    return arr.filter((val) => val.pid == pid);
  }

  let newArr = arr.map((val) => {
    if (getChildren(val.id).length > 0) {
      return { ...val, children: getChildren(val.id) };
    } else {
      return { ...val };
    }
  });

  return newArr
    .map((val) => {
      if (!idArr.includes(val.pid)) {
        return { ...val };
      }
    }).filter((item) => item);
}

3. 递归

const getChildren = (data, result, pid) => {
  let idArr = data.map((val) => val.id);

  for (const item of data) {
    if (item.pid === pid) {
      const newItem = { ...item, children: [] };
      if (!result.some((val) => val.id === newItem.id)) {
        result.push(newItem);
        getChildren(data, newItem.children, item.id);
      }
    }
  }
};

const arrChangeTree = (data) => {
  let idArr = data.map((val) => val.id);
  const result = [];
  for (let i = 0; i < data.length; i++) {
    if (!idArr.includes(data[i].pid)) {
      getChildren(data, result, data[i].pid);
    }
  }
  return result;
};