LeetCode/kt/max-sum-of-a-pair-with-equal-sum-of-digits.kt

class Solution {
    private fun digitSum(_num: Int): Int {
        var sum = 0

        var num = _num
        while (num > 0) {
            sum += num % 10
            num /= 10
        }

        return sum
    }

    fun maximumSum(nums: IntArray): Int =
        mutableMapOf<Int, Int>().let { best ->
            nums.withIndex().maxOf { num ->
                // find the digit sum
                val s = digitSum(num.value)

                // construct the sum of the maximum so far and current value
                val bestIndex = best.getOrDefault(s, -1)
                val currentSum =
                    when (bestIndex) {
                        -1 -> -1
                        else -> num.value + nums[bestIndex]
                    }

                // if found bigger value, update cached index
                if (bestIndex == -1 || num.value > nums[bestIndex]) {
                    best[s] = num.index
                }

                currentSum
            }
        }
}