diff --git a/binary-tree-level-order-traversal/ppxyn1.py b/binary-tree-level-order-traversal/ppxyn1.py
new file mode 100644
index 0000000000..ad58fc6175
--- /dev/null
+++ b/binary-tree-level-order-traversal/ppxyn1.py
@@ -0,0 +1,30 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+
+
+# idea: BFS 
+# Time Complexity: O(n)
+from collections import deque
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        ans = []
+        q = deque([root])
+        while q:
+            level = []
+            for i in range(len(q)):
+                node = q.popleft() 
+                if node:
+                    level.append(node.val) 
+                    if node.left:
+                        q.append(node.left) 
+                    if node.right:
+                        q.append(node.right) 
+            if level:
+                ans.append(level)
+        return ans
+
+
diff --git a/counting-bits/ppxyn1.py b/counting-bits/ppxyn1.py
new file mode 100644
index 0000000000..c163c5d001
--- /dev/null
+++ b/counting-bits/ppxyn1.py
@@ -0,0 +1,13 @@
+# idea : -
+# Time Complexity : O(n log n) since counting?
+class Solution:
+    def countBits(self, n: int) -> List[int]:
+        ans = []
+        for i in range(n + 1):
+            ans.append(bin(i)[2:].count("1"))
+        return ans
+
+# TODO: O(n)?
+
+
+
diff --git a/house-robber-ii/ppxyn1.py b/house-robber-ii/ppxyn1.py
new file mode 100644
index 0000000000..4873d10135
--- /dev/null
+++ b/house-robber-ii/ppxyn1.py
@@ -0,0 +1,27 @@
+# DP
+# Time Complexity : O(n)
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        if not nums:
+            return 0
+        if len(nums) == 1:
+            return nums[0]
+
+        # case 1: from start+1 to end
+        p1, p2 = 0, 0
+        for n in nums[1:]:
+            val = max(p1 + n, p2)
+            p1 = p2
+            p2 = val
+        case1 = p2
+
+        # case 2: from start to end-1
+        p1, p2 = 0, 0
+        for n in nums[:-1]:
+            val = max(p1 + n, p2)
+            p1 = p2
+            p2 = val
+        case2 = p2
+
+        return max(case1, case2)
+