FrequencyMap.kt

package utils

class FrequencyMap<K, Int>(private val b: MutableMap<K, kotlin.Int>)
    : MutableMap<K, kotlin.Int> by b {
      
    fun add(key: K, freq: kotlin.Int = 1) {
        b.computeIfPresent(key) { _, b -> b + freq }
        b.putIfAbsent(key, freq)
    }

    fun add(vararg pairs: Pair<K, kotlin.Int>) {
        for (pair in pairs) {
            val (key, freq) = pair
            add(key, freq)
        }
    }

    fun removeFreq(key: K, freq: kotlin.Int = 1) {
        if (b.get(key) == null || freq < 1) return
        else if (b.get(key)!! - freq < 1) b.remove(key)
        b.computeIfPresent(key) { _, b -> b - freq }
    }
}