Solution for https://leetcode.com/problems/two-sum/submissions/

TwoSumSolution.kt

class Solution {
    fun twoSum(nums: IntArray, target: Int): IntArray {
        val numberToIndexesMap = createNumberToIndexesMap(nums, target)
        // Iterate through each entry
        for (currEntry in numberToIndexesMap.entries) {
            // Subtract it from the target
            val nextValues = numberToIndexesMap[target - currEntry.key]

            if (nextValues == null || nextValues.isEmpty()) {
                continue
            }
            // And check if the subtracted value exists as key in the map
            if (nextValues.size > 1 || nextValues != currEntry.value) {
                val indexesForRemainingValue = numberToIndexesMap[target - currEntry.key]!!
                // If the subtracted value exists multiple times then choose 2nd element
                // Else choose first element
                return if (indexesForRemainingValue.size > 1) {
                    intArrayOf(currEntry.value[0], indexesForRemainingValue[1])
                } else {
                    intArrayOf(currEntry.value[0], indexesForRemainingValue[0])
                }
            }
        }
        return intArrayOf()
    }

    private fun createNumberToIndexesMap(
        arr: IntArray,
        expectedSum: Int
    ): MutableMap<Int, MutableList<Int>> {
        val numberToIndexesMap = mutableMapOf<Int, MutableList<Int>>()
        arr.withIndex().forEach {
            val num = it.value
            // Found another number with the same value as one of previous numbers
            if (numberToIndexesMap.containsKey(num)) {
                numberToIndexesMap[num]!!.add(it.index)
            } else {
                // First occurrence of number
                numberToIndexesMap[num] = mutableListOf(it.index)
            }
        }
        return numberToIndexesMap
    }
}