August LeetCoding Challenge Week 1: Day 6 (using negative substitution for O(n))

find_all_array_dups_using_negs.kt

import kotlin.math.abs 

class Solution {
    fun findDuplicates(nums: IntArray): List<Int> {
        fun twiceFound(acc: Pair<List<Int>, MutableList<Int>>, num: Int): Pair<List<Int>, MutableList<Int>> {
            val (uniques, negs) = acc
            return if (negs[abs(num) - 1] < 0) {
                uniques.plus(num) to negs
            } else {
                negs[abs(num) - 1] = -1 * negs[abs(num) - 1]
                uniques to negs
            }
        }
        

        val (twices, _) = nums.fold(listOf<Int>() to nums.toMutableList(), { t, num -> twiceFound(t, num) })
        
        return twices
        
    }
}

Results for find_all_array_dups.kt:

Results for find_all_array_dups_using_negs.kt: