kt: add «862. Shortest Subarray with Sum at Least K»

URL:	https://leetcode.com/problems/shortest-subarray-with-sum-at-least-k/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/shortest-subarray-with-sum-at-least-k.kt

@@ -0,0 +1,42 @@
+class Solution {
+    fun shortestSubarray(
+        nums: IntArray,
+        k: Int,
+    ): Int {
+        val sums =
+            nums
+                .scan(0L) { runningSum, x ->
+                    runningSum + x.toLong()
+                }
+                .toList()
+
+        val candidates = ArrayDeque<Int>()
+
+        return (0..nums.size)
+            .map { i ->
+                var shortestLength = Int.MAX_VALUE
+                while (
+                    candidates.isNotEmpty() &&
+                    sums[i] - sums[candidates.first()] >= k
+                ) {
+                    shortestLength =
+                        listOf(
+                            shortestLength, i - candidates.removeFirst(),
+                        ).min()
+                }
+
+                while (
+                    candidates.isNotEmpty() &&
+                    sums[i] <= sums[candidates.last()]
+                ) {
+                    candidates.removeLast()
+                }
+
+                candidates.add(i)
+
+                shortestLength
+            }
+            .filter { it < Int.MAX_VALUE }
+            .minOrNull() ?: -1
+    }
+}