kt: add «1975. Maximum Matrix Sum»

URL:	https://leetcode.com/problems/maximum-matrix-sum/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/maximum-matrix-sum.kt

@@ -0,0 +1,30 @@
+class Solution {
+    fun abs(x: Int): Int = listOf(x, -x).max()
+
+    private data class Accumulator(val sum: Long, val negatives: Int, val minimumAbs: Int) {
+        fun update(x: Int): Accumulator =
+            Accumulator(
+                sum + abs(x),
+                negatives +
+                    if (x < 0) {
+                        1
+                    } else {
+                        0
+                    },
+                listOf(minimumAbs, abs(x)).min(),
+            )
+
+        fun adjust(): Accumulator =
+            when {
+                negatives % 2 != 0 -> Accumulator(sum - 2 * minimumAbs, negatives, minimumAbs)
+                else -> this
+            }
+    }
+
+    fun maxMatrixSum(matrix: Array<IntArray>): Long =
+        matrix.fold(Accumulator(0L, 0, Int.MAX_VALUE)) { acc, row ->
+            row.fold(acc) { acc, it ->
+                acc.update(it)
+            }
+        }.adjust().sum
+}