diff --git a/climbing-stairs/bky373.java b/climbing-stairs/bky373.java
new file mode 100644
index 000000000..d5d8b2636
--- /dev/null
+++ b/climbing-stairs/bky373.java
@@ -0,0 +1,20 @@
+class Solution {
+
+    public int climbStairs(int n) {
+        if (n == 1) {
+            return n;
+        }
+        int a1 = 1;
+        int a2 = 2;
+        for (int i = 3; i < n + 1; i++) {
+            int a3 = a1 + a2;
+            a1 = a2;
+            a2 = a3;
+        }
+        return a2;
+    }
+}
+/**
+ * TC: O(N)
+ * SC: O(1)
+ */
diff --git a/maximum-depth-of-binary-tree/bky373.java b/maximum-depth-of-binary-tree/bky373.java
new file mode 100644
index 000000000..827dd86be
--- /dev/null
+++ b/maximum-depth-of-binary-tree/bky373.java
@@ -0,0 +1,17 @@
+/**
+ * TC: O(N)
+ * SC: O(N)
+ */
+class Solution {
+
+    public int maxDepth(TreeNode root) {
+        return findMax(root, 0);
+    }
+
+    public int findMax(TreeNode node, int depth) {
+        if (node == null) {
+            return depth;
+        }
+        return Math.max(findMax(node.left, depth + 1), findMax(node.right, depth + 1));
+    }
+}
diff --git a/meeting-rooms/bky373.java b/meeting-rooms/bky373.java
new file mode 100644
index 000000000..966ce64b0
--- /dev/null
+++ b/meeting-rooms/bky373.java
@@ -0,0 +1,19 @@
+class Solution {
+
+    public boolean canAttendMeetings(int[][] intervals) {
+        if (intervals.length == 0) {
+            return true;
+        }
+        Arrays.sort(intervals, (o1, o2) -> o1[0] - o2[0]);
+        for (int i = 0; i < intervals.length - 1; i++) {
+            if (intervals[i][1] > intervals[i + 1][0]) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+/**
+ * TC: O(nlogn), due to the sorting array.
+ * SC: O(1)
+ */
diff --git a/same-tree/bky373.java b/same-tree/bky373.java
new file mode 100644
index 000000000..88e3e0c4e
--- /dev/null
+++ b/same-tree/bky373.java
@@ -0,0 +1,11 @@
+/**
+ * TC: O(N)
+ * SC: O(N)
+ */
+class Solution {
+    public boolean isSameTree(TreeNode p, TreeNode q) {
+        if (p == null && q == null) return true;
+        if (p == null || q == null || p.val != q.val) return false;
+        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
+    }
+}
diff --git a/subtree-of-another-tree/bky373.java b/subtree-of-another-tree/bky373.java
new file mode 100644
index 000000000..7d6a4b2a0
--- /dev/null
+++ b/subtree-of-another-tree/bky373.java
@@ -0,0 +1,28 @@
+/**
+ * TC: O(M * N) - N: 메인 트리(root)의 노드 수, M: 서브 트리(subtree)의 노드 수
+ * SC: O(M + N)
+ * - isSubtree() 콜 스택은 최대 N 개 발생할 수 있고,
+ * - 각각 isSameTree() 콜 스택(M 개)을 더한 값까지 늘어날 수 있다.
+ * = isSameTree() 콜 스택은 호출 이후 사라지므로, 공간 복잡도는 최대 M + N 이다.
+ */
+class Solution {
+    public boolean isSubtree(TreeNode root, TreeNode subRoot) {
+        if (root == null) {
+            return false;
+        }
+        if (isSameTree(root, subRoot)) {
+            return true;
+        }
+        return isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot);
+    }
+
+    public boolean isSameTree(TreeNode n1, TreeNode n2) {
+        if (n1 == null || n2 == null) {
+            return n1 == n2;
+        }
+        if (n1.val != n2.val) {
+            return false;
+        }
+        return isSameTree(n1.left, n2.left) && isSameTree(n1.right, n2.right);
+    }
+}