从一个级别的对象列表中创建不带任何父级的树结构作为输入

const flatList = [
  { id: 1, name: 'A', parentId: null },
  { id: 2, name: 'B', parentId: 1 },
  { id: 3, name: 'C', parentId: 1 },
  { id: 4, name: 'D', parentId: 2 },
  { id: 5, name: 'E', parentId: 2 },
];

function buildTree(flatList) {
  const map = {};
  const roots = [];

  // 初始化map
  flatList.forEach(item => {
    map[item.id] = { ...item, children: [] };
  });

  // 构建树结构
  flatList.forEach(item => {
    if (item.parentId === null) {
      roots.push(map[item.id]);
    } else {
      map[item.parentId].children.push(map[item.id]);
    }
  });

  return roots;
}

const tree = buildTree(flatList);
console.log(JSON.stringify(tree, null, 2));

function buildTree(flatList) {
  const map = {};
  const roots = [];

  flatList.forEach(item => {
    map[item.id] = { ...item, children: [] };
  });

  flatList.forEach(item => {
    if (item.parentId === null) {
      roots.push(map[item.id]);
    } else {
      if (map[item.parentId]) {
        map[item.parentId].children.push(map[item.id]);
      } else {
        // 处理循环引用或无效的parentId
        console.error(`Invalid parentId ${item.parentId} for item ${item.id}`);
      }
    }
  });

  return roots;
}