Sort Characters By Frequency

Problem statement

Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string.

Return the sorted string. If there are multiple answers, return any of them.

Example 1:

Input: s = "tree"Output: "eert"Explanation: 'e' appears twice while 'r' and 't' both appear once.So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.

Example 2:

Input: s = "cccaaa"Output: "aaaccc"Explanation: Both 'c' and 'a' appear three times, so both "cccaaa" and "aaaccc" are valid answers.Note that "cacaca" is incorrect, as the same characters must be together.

Example 3:

Input: s = "Aabb"Output: "bbAa"Explanation: "bbaA" is also a valid answer, but "Aabb" is incorrect.Note that 'A' and 'a' are treated as two different characters.

Constraints:

• 1 <= s.length <= 5 * 105
• s consists of uppercase and lowercase English letters and digits.

My solution

/**
 * @param {string} s
 * @return {string}
 */
var frequencySort = function(s) {
    const memo = new Map();
    
    for (const a of s) {
        if (!memo.has(a)) {
            memo.set(a, 0)
        }
        memo.set(a, memo.get(a) + 1)
    }
    
    const items = [...memo].sort((a, b) => b[1] - a[1]);
    
    // console.log(items)
    
    return items.reduce((acc, [char, count]) => {
        acc += Array.from({
            length: count
        }, () => char).join("")
        
        return acc;
    }, "")
    
};