kt: add «1524. Number of Sub-arrays With Odd Sum»

URL:	https://leetcode.com/problems/number-of-sub-arrays-with-odd-sum/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/number-of-sub-arrays-with-odd-sum.kt

@@ -0,0 +1,32 @@
+class Solution {
+    companion object {
+        private val MOD: Int = 1_000_000_007
+    }
+
+    private data class Acc(val count: Int, val sum: Int, val odd: Int, val even: Int) {
+        constructor() : this(0, 0, 0, 1) {}
+
+        fun update(num: Int): Acc =
+            (sum + num).let { sum ->
+                when {
+                    sum % 2 == 0 ->
+                        this.copy(
+                            count = (count + odd) % MOD,
+                            sum = sum,
+                            even = even + 1,
+                        )
+                    else ->
+                        this.copy(
+                            count = (count + even) % MOD,
+                            sum = sum,
+                            odd = odd + 1,
+                        )
+                }
+            }
+    }
+
+    fun numOfSubarrays(arr: IntArray): Int =
+        arr.fold(Acc()) { acc, it ->
+            acc.update(it)
+        }.count
+}