Add goodie for pre-order of an n-ary tree

Closes #396.

Author: skdthread

workspaces/adventure-pack/goodies/typescript/traversePreOrderNAry/index.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, it } from "@jest/globals";
+
+import { traversePreOrderNAry } from "./index.ts";
+
+type Node = { val: number; children: Node[] };
+
+describe("traversePreOrderNAry", () => {
+  it("returns empty for null root", () => {
+    expect([...traversePreOrderNAry(null)]).toStrictEqual([]);
+  });
+
+  it("returns empty for undefined root", () => {
+    expect([...traversePreOrderNAry(undefined)]).toStrictEqual([]);
+  });
+
+  it("yields root only for single node", () => {
+    const root: Node = { val: 1, children: [] };
+    expect([...traversePreOrderNAry(root)].map((n) => n.val)).toStrictEqual([
+      1,
+    ]);
+  });
+
+  it("visits parent before children", () => {
+    const root: Node = {
+      val: 1,
+      children: [{ val: 2, children: [] }, { val: 3, children: [] }],
+    };
+    expect([...traversePreOrderNAry(root)].map((n) => n.val)).toStrictEqual([
+      1, 2, 3,
+    ]);
+  });
+
+  it("traverses deeper trees in pre-order", () => {
+    const root: Node = {
+      val: 1,
+      children: [
+        {
+          val: 2,
+          children: [
+            { val: 4, children: [] },
+            { val: 5, children: [] },
+          ],
+        },
+        { val: 3, children: [] },
+      ],
+    };
+    expect([...traversePreOrderNAry(root)].map((n) => n.val)).toStrictEqual([
+      1, 2, 4, 5, 3,
+    ]);
+  });
+});

workspaces/adventure-pack/goodies/typescript/traversePreOrderNAry/index.ts

@@ -0,0 +1,17 @@
+export function* traversePreOrderNAry<T extends { children: T[] }>(
+  root: T | null | undefined,
+): Generator<T, void, void> {
+  if (root == null) {
+    return;
+  }
+
+  const stack: T[] = [root];
+
+  do {
+    const node = stack.pop()!;
+    yield node;
+    for (let i = node.children.length - 1; i >= 0; --i) {
+      stack.push(node.children[i]);
+    }
+  } while (stack.length > 0);
+}