LeetCode/kt/find-missing-and-repeated-values.kt

class Solution {
    fun findMissingAndRepeatedValues(grid: Array<IntArray>): IntArray {
        val n = grid.size.toLong()
        val n2 = n.toLong() * n

        val (sum, sumOfSquares) =
            grid.fold(0L to 0L) { acc, row ->
                row.fold(acc) { (sum, sumOfSquares), x ->
                    sum + x to sumOfSquares + x * x
                }
            }

        val sumDiff = sum - n2 * (n2 + 1) / 2
        val sqrDiff = sumOfSquares - n2 * (n2 + 1) * (2 * n2 + 1) / 6

        val repeating = ((sqrDiff / sumDiff + sumDiff) / 2).toInt()
        val missing = ((sqrDiff / sumDiff - sumDiff) / 2).toInt()

        return intArrayOf(repeating, missing)
    }
}