计数排序

let countSort = arr => {
  let hashTable = {}, max = 0,result = [];
  for (let i = 0; i < arr.length; i++) {
    if( !(i in hashTable) ) {
      hashTable[arr[i]] = 1;
    } else {
      hashTable[arr[i]] += 1;
    }
    if(arr[i]> max) {
      max = arr[i]
    }
  }
 
 for (let key in hashTable) {
    console.log(typeof key); // key 为 string
  }
  console.log(hashTable['4'] === hashTable[4]); //true

  for (let j = 0; j <= max; j++) {
    if (j in hashTable) {
      result.push(j)
    }
  }
  //j的类型为number, push到result
  console.log(typeof result);
  return result;
};
countSort([9,7,5,7,4,8,4,6,8,3,5,0]);