diff --git a/climbing-stairs/saysimple.py b/climbing-stairs/saysimple.py
new file mode 100644
index 000000000..02c6f57a9
--- /dev/null
+++ b/climbing-stairs/saysimple.py
@@ -0,0 +1,10 @@
+## TC: O(n), SC:O(1)
+
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        a, b = 1, 1
+
+        for i in range(n - 1):
+            a, b = a + b, a
+
+        return a
diff --git a/maximum-depth-of-binary-tree/saysimple.py b/maximum-depth-of-binary-tree/saysimple.py
new file mode 100644
index 000000000..741cee74a
--- /dev/null
+++ b/maximum-depth-of-binary-tree/saysimple.py
@@ -0,0 +1,11 @@
+# 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
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))
diff --git a/meeting-rooms/saysimple.py b/meeting-rooms/saysimple.py
new file mode 100644
index 000000000..14b785863
--- /dev/null
+++ b/meeting-rooms/saysimple.py
@@ -0,0 +1,16 @@
+# TC: O(n), SC: O(1)
+class Solution:
+    def canAttendMeetings(self, intervals: List[Interval]) -> bool:
+        if not intervals:
+            return True
+
+        intervals.sort(key=lambda x: x.start)
+
+        e = intervals[0].end
+
+        for i in range(1, len(intervals)):
+            if intervals[i].start < e:
+                return False
+            e = intervals[i].end
+
+        return True
diff --git a/same-tree/saysimple.py b/same-tree/saysimple.py
new file mode 100644
index 000000000..c95fe9ff9
--- /dev/null
+++ b/same-tree/saysimple.py
@@ -0,0 +1,27 @@
+# TC: O(n), SC:O(n)
+# 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
+class Solution:
+    t = []
+    def pre_order(self, node: TreeNode):
+        if node is None:
+            self.t.append(None)
+            return
+
+        self.t.append(node.val)
+        self.pre_order(node.left)
+        self.pre_order(node.right)
+
+    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
+        self.t = []
+        self.pre_order(p)
+        a = self.t[:]
+        self.t = []
+        self.pre_order(q)
+        b = self.t[:]
+
+        return a == b
diff --git a/subtree-of-another-tree/saysimple.py b/subtree-of-another-tree/saysimple.py
new file mode 100644
index 000000000..e81ed7add
--- /dev/null
+++ b/subtree-of-another-tree/saysimple.py
@@ -0,0 +1,23 @@
+# TC: O(mn), SC: O(m+n)
+# 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
+class Solution:
+    def isSubtree(self, root: Optional[TreeNode], subRoot: Optional[TreeNode]) -> bool:
+        def prev(root, subRoot):
+            if not root or not subRoot:
+                return root == subRoot
+            if root.val != subRoot.val:
+                return False
+
+            return prev(root.left, subRoot.left) and prev(root.right, subRoot.right)
+
+        if not root:
+            return False
+        if prev(root, subRoot):
+            return True
+
+        return self.isSubtree(root.left, subRoot) or self.isSubtree(root.right, subRoot)