Data commit

Task/Power-set/Kotlin/power-set.kotlin

@@ -0,0 +1,26 @@
+// purely functional & lazy version, leveraging recursion and Sequences (a.k.a. streams)
+fun <T> Set<T>.subsets(): Sequence<Set<T>> =
+    when (size) {
+        0 -> sequenceOf(emptySet())
+        else -> {
+            val head = first()
+            val tail = this - head
+            tail.subsets() + tail.subsets().map { setOf(head) + it }
+        }
+    }
+
+// if recursion is an issue, you may change it this way:
+
+fun <T> Set<T>.subsets(): Sequence<Set<T>> = sequence {
+    when (size) {
+        0 -> yield(emptySet<T>())
+        else -> {
+            val head = first()
+            val tail = this@subsets - head
+            yieldAll(tail.subsets())
+            for (subset in tail.subsets()) {
+                yield(setOf(head) + subset)
+            }
+        }
+    }
+}