From 428e617fe1b1c1bca2ec766e65df8c062e5430ed Mon Sep 17 00:00:00 2001
From: Jeongwon Na <ge95lis@tum.de>
Date: Mon, 20 Oct 2025 16:26:09 +0200
Subject: [PATCH 1/2] counting bits solution

---
 counting-bits/njngwn.java | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 counting-bits/njngwn.java

diff --git a/counting-bits/njngwn.java b/counting-bits/njngwn.java
new file mode 100644
index 000000000..8619c9fbd
--- /dev/null
+++ b/counting-bits/njngwn.java
@@ -0,0 +1,11 @@
+class Solution {
+    public int[] countBits(int n) {
+        int[] bitCountArr = new int[n+1];
+
+        for (int i = 1; i <= n; ++i) {
+            bitCountArr[i] = bitCountArr[i/2] + (i & 1);
+        }
+
+        return bitCountArr;
+    }
+}

From bdfad3609e68c6fd80299cd1bbb48abc64703a6c Mon Sep 17 00:00:00 2001
From: Jeongwon Na <ge95lis@tum.de>
Date: Mon, 20 Oct 2025 16:29:13 +0200
Subject: [PATCH 2/2] binary-tree-level-order-traversal solution

---
 binary-tree-level-order-traversal/njngwn.java | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 binary-tree-level-order-traversal/njngwn.java

diff --git a/binary-tree-level-order-traversal/njngwn.java b/binary-tree-level-order-traversal/njngwn.java
new file mode 100644
index 000000000..5d55d4981
--- /dev/null
+++ b/binary-tree-level-order-traversal/njngwn.java
@@ -0,0 +1,43 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    // Time Complexity: O(n), n: the number of nodes
+    // Space Complexity: O(w), w: max width of tree
+
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> results = new ArrayList<>();
+        if (root == null) return results;
+
+        Queue<TreeNode> levelQueue = new LinkedList<>();    // use queue considering FIFO
+        levelQueue.offer(root);
+
+        while (!levelQueue.isEmpty()) {
+            ArrayList<Integer> level = new ArrayList<>();   // node values list for each level
+            int size = levelQueue.size();
+
+            for (int i = 0; i < size; ++i) {
+                TreeNode node = levelQueue.poll();
+                level.add(node.val);
+                if(node.left != null) levelQueue.offer(node.left);
+                if(node.right != null) levelQueue.offer(node.right);
+            }
+
+            results.add(level);
+        }
+
+        return results;
+    }
+}