Refactor (2)

packages/utils/src/array.ts

@@ -1,7 +1,9 @@
+/** Returns a random element of the array  */
 export const sample = <T>(arr: readonly T[]): T =>
   arr[Math.floor(Math.random() * arr.length)] as T;
 
-export function sampleMany<T>(arr: T[], n: number = arr.length): T[] {
+/** Returns random N elements of the array  */
+export function sampleMany<T>(arr: readonly T[], n: number = arr.length): T[] {
   if (n > arr.length) return sampleMany(arr, arr.length);
   const copy = [...arr];
   for (let i = 0; i < n; i++) {
@@ -10,3 +12,47 @@ export function sampleMany<T>(arr: T[], n: number = arr.length): T[] {
   }
   return copy.slice(0, n);
 }
+
+/** Returns a powerset of the array */
+export const power = <T>(arr: readonly T[]) =>
+  arr.reduce((a, v) => a.concat(a.map((r) => r.concat(v))), [[]] as T[][]);
+
+/** Returns all the permutations of the array */
+export function permutate<T>(arr: readonly T[]): T[][] {
+  if (arr.length === 0) return [[]];
+  const result: T[][] = [];
+  for (let i = 0; i < arr.length; i++) {
+    const current = arr[i];
+    const remaining = [...arr.slice(0, i), ...arr.slice(i + 1)];
+    for (const perm of permutate(remaining)) {
+      result.push([current as T, ...perm]);
+    }
+  }
+  return result;
+}
+
+/** Returns the maximal elements of the array w.r.t. the preorder */
+export function maximal<T>(
+  arr: readonly T[],
+  preorder: (x: T, y: T) => boolean,
+): T[] {
+  const res: T[] = [];
+  outer: for (const x of arr) {
+    for (let i = 0; i < res.length; ) {
+      const y = res[i] as T;
+      const xLeY = preorder(x, y);
+      const yLeX = preorder(y, x);
+
+      if (xLeY) {
+        continue outer;
+      }
+      if (yLeX) {
+        res.splice(i, 1);
+        continue;
+      }
+      i++;
+    }
+    res.push(x);
+  }
+  return res;
+}