SOURCE

//查找⼀个字符串⾥出现次数最多的字符
//对以下数组按年龄从⼤到⼩进⾏排序，并统计出各个不同职业的总⼈数

const arr = [
{
name: "张三",
age: 23,
profession: "医生"
},
{
name: "李四",
age: 30,
profession: "演员"
},
{
name: "熊大",
age: 18,
profession: "运动员"
},
{
name: "小陈",
age: 28,
profession: "医生"
}
]
//q2: sourceData 转换成 treeData
const sourceData = [
  { province: "广东省", city: "深圳市", country: "宝安区" },
  { province: "广东省", city: "深圳市", country: "南山区" },
  { province: "广东省", city: "深圳市", country: "罗湖区" },
  { province: "广东省", city: "深圳市", country: "福田区" },
  { province: "四川省", city: "成都市", country: "金牛区" },
];
const treeData = [
  {
    name: "广东省",
    children: [
      {
        name: "深圳市",
        children: [
          { name: "宝安区" },
          { name: "南山区" },
          { name: "罗湖区" },
          { name: "福田区" },
        ],
      },
    ],
  },
  {
    name: "四川省",
    children: [{ name: "成都市", children: [{ name: "金牛区" }] }],
  },
];
const keys = ["province", "city", "country"];