init: add source code from src.zip

src/utils/array.ts

@@ -0,0 +1,13 @@
+export function intersperse<A>(as: A[], separator: (index: number) => A): A[] {
+  return as.flatMap((a, i) => (i ? [separator(i), a] : [a]))
+}
+
+export function count<T>(arr: readonly T[], pred: (x: T) => unknown): number {
+  let n = 0
+  for (const x of arr) n += +!!pred(x)
+  return n
+}
+
+export function uniq<T>(xs: Iterable<T>): T[] {
+  return [...new Set(xs)]
+}