From 1b9766167704f4806e76c64a1a6904fe4aa0b99c Mon Sep 17 00:00:00 2001
From: TheGeniusOfEternity <max06safin@yandex.ru>
Date: Thu, 27 Aug 2026 15:57:22 +0300
Subject: [PATCH 1/4] test(neetcode|interview|find-by-type): testcases

---
 src/interview/find-by-type/solution.test.ts | 113 ++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 src/interview/find-by-type/solution.test.ts

diff --git a/src/interview/find-by-type/solution.test.ts b/src/interview/find-by-type/solution.test.ts
new file mode 100644
index 0000000..9a1632c
--- /dev/null
+++ b/src/interview/find-by-type/solution.test.ts
@@ -0,0 +1,113 @@
+import { findByType } from './solution';
+
+describe('Find By Type | Interview | Testcases', () => {
+  test('#1 Follow upside-down order', () => {
+    const tree = {
+      type: 'folder',
+      name: 'root',
+      children: [
+        { type: 'file', name: 'file-1', children: [] },
+        {
+          type: 'folder',
+          name: 'docs',
+          children: [{ type: 'file', name: 'file-2', children: [] }],
+        },
+        { type: 'file', name: 'file-3', children: [] },
+      ],
+    };
+    expect(findByType(tree, 'file').map((node) => node.name)).toEqual([
+      'file-1',
+      'file-2',
+      'file-3',
+    ]);
+  });
+
+  test('#2 No nodes of requested type', () => {
+    const tree = {
+      type: 'folder',
+      name: 'root',
+      children: [
+        { type: 'folder', name: 'sub1', children: [] },
+        { type: 'folder', name: 'sub2', children: [] },
+      ],
+    };
+    expect(findByType(tree, 'file')).toEqual([]);
+  });
+
+  test('#3 All nodes are of requested type', () => {
+    const tree = {
+      type: 'file',
+      name: 'root-file',
+      children: [
+        { type: 'file', name: 'file-a', children: [] },
+        { type: 'file', name: 'file-b', children: [] },
+      ],
+    };
+    expect(findByType(tree, 'file').map((node) => node.name)).toEqual([
+      'root-file',
+      'file-a',
+      'file-b',
+    ]);
+  });
+
+  test('#4 Deep nesting', () => {
+    const tree = {
+      type: 'folder',
+      name: 'root',
+      children: [
+        {
+          type: 'folder',
+          name: 'level1',
+          children: [
+            {
+              type: 'folder',
+              name: 'level2',
+              children: [{ type: 'file', name: 'deep-file', children: [] }],
+            },
+          ],
+        },
+      ],
+    };
+    expect(findByType(tree, 'file').map((node) => node.name)).toEqual([
+      'deep-file',
+    ]);
+  });
+
+  test('#5 Multiple matches in different branches', () => {
+    const tree = {
+      type: 'folder',
+      name: 'root',
+      children: [
+        {
+          type: 'folder',
+          name: 'branch1',
+          children: [
+            { type: 'file', name: 'b1-f1', children: [] },
+            { type: 'file', name: 'b1-f2', children: [] },
+          ],
+        },
+        {
+          type: 'folder',
+          name: 'branch2',
+          children: [{ type: 'file', name: 'b2-f1', children: [] }],
+        },
+      ],
+    };
+    expect(findByType(tree, 'file').map((node) => node.name)).toEqual([
+      'b1-f1',
+      'b1-f2',
+      'b2-f1',
+    ]);
+  });
+
+  test('#6 Search for type that appears only in root', () => {
+    const tree = {
+      type: 'special',
+      name: 'root-special',
+      children: [{ type: 'file', name: 'file-1', children: [] }],
+    };
+    expect(findByType(tree, 'special').map((node) => node.name)).toEqual([
+      'root-special',
+    ]);
+  });
+});

From 3094aad21c2622adb882100097a4c332e896ba8a Mon Sep 17 00:00:00 2001
From: TheGeniusOfEternity <max06safin@yandex.ru>
Date: Thu, 27 Aug 2026 15:57:34 +0300
Subject: [PATCH 2/4] feat(neetcode|interview|find-by-type): recursive solution

---
 src/interview/find-by-type/solution.ts | 43 ++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 src/interview/find-by-type/solution.ts

diff --git a/src/interview/find-by-type/solution.ts b/src/interview/find-by-type/solution.ts
new file mode 100644
index 0000000..269173e
--- /dev/null
+++ b/src/interview/find-by-type/solution.ts
@@ -0,0 +1,43 @@
+interface Tree {
+  type: string;
+  name: string;
+  children: Tree[];
+}
+
+/**
+ * @param tree - nested object of nodes
+ * @param type - searching param to find nodes
+ *
+ * @example
+ *
+ * const tree = {
+ *   type: 'folder',
+ *   name: 'root',
+ *   children: [
+ *     { type: 'file', name: 'file-1', children: [] },
+ *     {
+ *       type: 'folder',
+ *       name: 'docs',
+ *       children: [{ type: 'file', name: 'file-2', children: [] }],
+ *     },
+ *     { type: 'file', name: 'file-3', children: [] },
+ *   ],
+ * };
+ *
+ * console.log(findByType(tree, 'file').map((node) => node.name));
+ * // Expected: ["file-1", "file-2", "file-3"]
+ */
+export const findByType = (tree: Tree, type: string): Tree[] => {
+  const matches: Tree[] = [];
+  const dfs = (node: Tree): void => {
+    if (node.type === type) {
+      matches.push(node);
+    }
+    node.children.forEach((child: Tree) => {
+      dfs(child);
+    });
+  };
+  dfs(tree);
+
+  return matches;
+};

From ede68545569a78dfff6aefc20f8547e5ac73163a Mon Sep 17 00:00:00 2001
From: TheGeniusOfEternity <max06safin@yandex.ru>
Date: Thu, 27 Aug 2026 16:00:21 +0300
Subject: [PATCH 3/4] feat(neetcode|interview|find-by-type): iterative solution

---
 src/interview/find-by-type/solution.ts | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/interview/find-by-type/solution.ts b/src/interview/find-by-type/solution.ts
index 269173e..c96fe43 100644
--- a/src/interview/find-by-type/solution.ts
+++ b/src/interview/find-by-type/solution.ts
@@ -29,15 +29,20 @@ interface Tree {
  */
 export const findByType = (tree: Tree, type: string): Tree[] => {
   const matches: Tree[] = [];
-  const dfs = (node: Tree): void => {
-    if (node.type === type) {
-      matches.push(node);
+  const stack: Tree[] = [tree];
+
+  while (stack.length) {
+    const node = stack.pop();
+    if (node) {
+      if (node.type === type) {
+        matches.push(node);
+      }
+
+      for (let i = node.children.length - 1; i >= 0; i--) {
+        stack.push(node.children[i]);
+      }
     }
-    node.children.forEach((child: Tree) => {
-      dfs(child);
-    });
-  };
-  dfs(tree);
+  }
 
   return matches;
 };

From 951b7080832189068ce94001274a19cabed403a9 Mon Sep 17 00:00:00 2001
From: TheGeniusOfEternity <max06safin@yandex.ru>
Date: Thu, 27 Aug 2026 16:00:32 +0300
Subject: [PATCH 4/4] feat(neetcode|interview): update table of contents

---
 README.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index f06bd83..ef9e775 100644
--- a/README.md
+++ b/README.md
@@ -132,4 +132,5 @@ Interview Questions
 - [Task #10](src/interview/render-items/with-async) - _Render Items: With Async_
 - [Task #11](src/interview/build-tree/no-replies-sort) - _Build Tree: No Replies Sort_
 - [Task #12](src/interview/build-tree/with-replies-sort) - _Build Tree: With Replies Sort_
-- [Task #13](src/interview/build-comments-tree) - _Build Comments Tree_
\ No newline at end of file
+- [Task #13](src/interview/build-comments-tree) - _Build Comments Tree_
+- [Task #13](src/interview/find-by-type) - _Find By Type_
\ No newline at end of file