kt: add «2965. Find Missing and Repeated Values»

URL:	https://leetcode.com/problems/find-missing-and-repeated-values/
Signed-off-by: Matej Focko <me@mfocko.xyz>

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

@@ -0,0 +1,21 @@
+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)
+    }
+}