kt: add «1718. Construct the Lexicographically Largest Valid Sequence»

URL:	https://leetcode.com/problems/construct-the-lexicographically-largest-valid-sequence/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/construct-the-lexicographically-largest-valid-sequence.kt

@@ -0,0 +1,48 @@
+class Solution {
+    private data class LargestSequence(val n: Int) {
+        val result: IntArray = IntArray(n * 2 - 1) { 0 }
+        private val isUsed: BooleanArray = BooleanArray(n + 1) { false }
+
+        fun find(i: Int): Boolean =
+            when {
+                // All positions were filled
+                i == result.size -> true
+
+                // Already filled, can skip
+                result[i] != 0 -> find(i + 1)
+                else -> {
+                    (n downTo 1).asSequence().filter {
+                        !isUsed[it]
+                    }.forEach { toPlace ->
+                        isUsed[toPlace] = true
+                        result[i] = toPlace
+
+                        if (toPlace == 1) {
+                            if (find(i + 1)) {
+                                return true
+                            }
+                        } else if (i + toPlace < result.size && result[i + toPlace] == 0) {
+                            result[i + toPlace] = toPlace
+
+                            if (find(i + 1)) {
+                                return true
+                            }
+
+                            result[i + toPlace] = 0
+                        }
+
+                        result[i] = 0
+                        isUsed[toPlace] = false
+                    }
+
+                    false
+                }
+            }
+    }
+
+    fun constructDistancedSequence(n: Int): IntArray =
+        LargestSequence(n).let {
+            it.find(0)
+            it.result
+        }
+}