SortCharactersByFrequency.js

/*Given a string, sort it in decreasing order based on the frequency of characters.

Example 1:

Input:
"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:
"cccaaa"

Output:
"cccaaa"

Explanation:
Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
Note that "cacaca" is incorrect, as the same characters must be together.
Example 3:

Input:
"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.*/

var frequencySort = function(s) {
    const hmap = {}
    for (let i = 0; i < s.length; i++) {
        const char = s.charAt(i)
        hmap[char] = hmap[char] + 1 || 1
    }
    const sorted = Object.keys(hmap).sort((a, b) => hmap[b] - hmap[a])
    let result = ''
    for (let i = 0; i < sorted.length; i++) {
        const char = sorted[i]
        result += char.repeat(hmap[char])
    }
    return  result
};