K Unique String - KOTLIN

// Author : Saurav Kalsoor
// K Unique String - KOTLIN

import java.util.*;

var sc = Scanner(System.`in`)

fun main() {
    val s = sc.next()
    val k = sc.nextInt()
    println(kUniqueString(s, k))
}

fun kUniqueString(s: String, k: Int): Int {
    val freq = HashMap<Char, Int>()
    for (i in 0 until s.length) {
        freq[s[i]] = freq.getOrDefault(s[i], 0) + 1
    }
    val st: MutableSet<MyPair> =
        TreeSet { a, b ->
            if (a.frequency == b.frequency)
                a.ch - b.ch
            else
                a.frequency - b.frequency
        }

    for ((key, value) in freq) {
        st.add(MyPair(key, value))
    }
    var distinct = freq.size
    var changes = 0
    for (x in st) {
        if (distinct <= k) break
        changes += x.frequency
        distinct--
    }
    return changes
}

internal class MyPair(var ch: Char, var frequency: Int)