平铺行政区

[
  {
    "id": 1,
    "code": "350400",
    "name": "三明市",
    "grade": "city",
    "orderNo": 1,
    "parentCode": null,
    "children": [
      {
        "id": 8,
        "code": "350426",
        "name": "尤溪县",
        "grade": "county",
        "orderNo": 7,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 12,
        "code": "350430",
        "name": "建宁县",
        "grade": "county",
        "orderNo": 11,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 11,
        "code": "350429",
        "name": "泰宁县",
        "grade": "county",
        "orderNo": 10,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 9,
        "code": "350427",
        "name": "沙县",
        "grade": "county",
        "orderNo": 8,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 2,
        "code": "350402",
        "name": "梅列区",
        "grade": "county",
        "orderNo": 1,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 4,
        "code": "350421",
        "name": "明溪县",
        "grade": "county",
        "orderNo": 3,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 7,
        "code": "350425",
        "name": "大田县",
        "grade": "county",
        "orderNo": 6,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 5,
        "code": "350423",
        "name": "清流县",
        "grade": "county",
        "orderNo": 4,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 10,
        "code": "350428",
        "name": "将乐县",
        "grade": "county",
        "orderNo": 9,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 13,
        "code": "350481",
        "name": "永安市",
        "grade": "county",
        "orderNo": 12,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 3,
        "code": "350403",
        "name": "三元区",
        "grade": "county",
        "orderNo": 2,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 6,
        "code": "350424",
        "name": "宁化县",
        "grade": "county",
        "orderNo": 5,
        "parentCode": "350400",
        "children": []
      }
    ]
  }
]

export function flatDistricts(districts: District[]): District[] {
    let flattedDistricts = districts.slice(0)
    for (let i = 0; i < flattedDistricts.length; i++) {
        let d = flattedDistricts[i]
        if (d.children.length > 0) {
            flattedDistricts = flattedDistricts.concat(d.children)
        }
    }
    return flattedDistricts
}