[LeetCode] 451 - Sort Characters By Frequency

題意

改變輸入的字串為出現頻率高至低，若頻率相同則照字典排序。

程式

/**
 * @param {string} s
 * @return {string}
 */
var frequencySort = function(s) {
  let map = {};
  for (let i = 0; i < s.length; i ++ ){
    map[s[i]] = map[s[i]] === undefined ? 1 : map[s[i]] + 1 ;
  }
  return Object.keys(map)
    .map(key => {
      return { key : key , amount : map[key] };
    })
    .sort((e1, e2) => {
      if ( e1.amount !== e2.amount ) return e2.amount - e1.amount;
      else return e1.key < e2.key ? -1 : 1;
    })
    .reduce((cal, el) => cal + Array(el.amount+1).join(el.key), "")
};