diff --git a/binary-tree-level-order-traversal/Tessa1217.java b/binary-tree-level-order-traversal/Tessa1217.java
new file mode 100644
index 000000000..406e49fdb
--- /dev/null
+++ b/binary-tree-level-order-traversal/Tessa1217.java
@@ -0,0 +1,87 @@
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+/**
+ * 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 {
+
+    // DFS 풀이
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> result = new ArrayList<>();
+        dfs(root, 0, result);
+        return result;
+    }
+
+    private void dfs(TreeNode node, int depth, List<List<Integer>> result) {
+        if (node == null) {
+            return;
+        }
+
+        // 깊이만큼의 리스트가 없으면 새 리스트 추가하기
+        if (depth == result.size()) {
+            result.add(new ArrayList<>());
+        }
+
+        result.get(depth).add(node.val);
+
+        dfs(node.left, depth + 1, result);
+        dfs(node.right, depth + 1, result);
+
+
+    }
+
+    // BFS로 풀이
+    // O(n)
+//    public List<List<Integer>> levelOrder(TreeNode root) {
+//
+//        List<List<Integer>> result = new ArrayList<>();
+//
+//        if (root == null) {
+//            return result;
+//        }
+//
+//        Queue<TreeNode> queue = new LinkedList<>();
+//        queue.offer(root);
+//
+//        while (!queue.isEmpty()) {
+//            int nodeCnt = queue.size();
+//            List<Integer> currentLevelNodes = new ArrayList<>();
+//
+//            for (int i = 0; i < nodeCnt; i++) {
+//                TreeNode current = queue.poll();
+//                currentLevelNodes.add(current.val);
+//
+//                if (current.left != null) {
+//                    queue.offer(current.left);
+//                }
+//
+//                if (current.right != null) {
+//                    queue.offer(current.right);
+//                }
+//
+//            }
+//
+//            result.add(currentLevelNodes);
+//
+//        }
+//
+//        return result;
+//
+//    }
+}
+
diff --git a/counting-bits/Tessa1217.java b/counting-bits/Tessa1217.java
new file mode 100644
index 000000000..3b020e4d7
--- /dev/null
+++ b/counting-bits/Tessa1217.java
@@ -0,0 +1,14 @@
+class Solution {
+
+    // 시간복잡도: O(n)
+    public int[] countBits(int n) {
+        int[] bitsArray = new int[n + 1];
+        for (int i = 1; i <= n; i++) {
+            // Shift 연산자 사용
+            // i&1 => 마지막 비트가 0인지 1인지 확인
+            bitsArray[i] = bitsArray[i >> 1] + (i & 1);
+        }
+        return bitsArray;
+    }
+}
+
diff --git a/find-median-from-data-stream/Tessa1217.java b/find-median-from-data-stream/Tessa1217.java
new file mode 100644
index 000000000..ff717faf6
--- /dev/null
+++ b/find-median-from-data-stream/Tessa1217.java
@@ -0,0 +1,46 @@
+import java.util.PriorityQueue;
+
+class MedianFinder {
+
+    // 작은 수 범위 저장하는 힙
+    private PriorityQueue<Integer> smallHeap;
+
+    // 큰 수 범위 저장하는 힙
+    private PriorityQueue<Integer> largeHeap;
+
+    public MedianFinder() {
+        smallHeap = new PriorityQueue<>((a, b) -> b - a);
+        largeHeap = new PriorityQueue<> ((a, b) -> a - b);
+    }
+
+    public void addNum(int num) {
+        // 작은 수 범위에 삽입
+        smallHeap.offer(num);
+        // 작은 수 범위에서 최댓값을 뽑아 큰 수 범위로 이동
+        largeHeap.offer(smallHeap.poll());
+
+        // 만약 작은 수 범위의 개수가 큰 수 범위보다 작다면
+        if (smallHeap.size() < largeHeap.size()) {
+            // 큰 수 범위에서 최솟값을 뽑아 작은 수 범위로 이동
+            smallHeap.offer(largeHeap.poll());
+        }
+    }
+
+    public double findMedian() {
+        // 짝수 개일 경우
+        if (smallHeap.size() == largeHeap.size()) {
+            // 작은 수 범위 힙의 최댓값 + 큰 수 범위 힙의 최솟값의 평균
+            return (smallHeap.peek() + largeHeap.peek()) / 2.0;
+        }
+        // 작은 수 범위 힙의 최댓값
+        return smallHeap.peek();
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * MedianFinder obj = new MedianFinder();
+ * obj.addNum(num);
+ * double param_2 = obj.findMedian();
+ */
+
diff --git a/house-robber-ii/Tessa1217.java b/house-robber-ii/Tessa1217.java
new file mode 100644
index 000000000..2014b0e40
--- /dev/null
+++ b/house-robber-ii/Tessa1217.java
@@ -0,0 +1,45 @@
+class Solution {
+
+    // DP
+    public int rob(int[] nums) {
+        int n = nums.length;
+
+        if (n == 0) {
+            return 0;
+        }
+
+        if (n == 1) {
+            return nums[0];
+        }
+
+        int notRobbingLast = robHouses(nums, 0, n - 2);
+        int notRobbingFirst = robHouses(nums, 1, n - 1);
+
+        return Math.max(notRobbingLast, notRobbingFirst);
+    }
+
+    private int robHouses(int[] nums, int start, int end) {
+
+        int length = end - start + 1;
+
+        if (length == 0) {
+            return 0;
+        }
+
+        if (length == 1) {
+            return nums[start];
+        }
+
+        int[] dp = new int[length];
+
+        dp[0] = nums[start];
+        dp[1] = Math.max(nums[start], nums[start + 1]);
+
+        for (int i = 2; i < length; i++) {
+            dp[i] = Math.max(dp[i - 2] + nums[start + i], dp[i - 1]);
+        }
+
+        return dp[length - 1];
+    }
+}
+
diff --git a/insert-interval/Tessa1217.java b/insert-interval/Tessa1217.java
new file mode 100644
index 000000000..8e14916ab
--- /dev/null
+++ b/insert-interval/Tessa1217.java
@@ -0,0 +1,39 @@
+import java.util.ArrayList;
+import java.util.List;
+
+class Solution {
+
+    // 시간, 공간복잡도: O(n)
+    public int[][] insert(int[][] intervals, int[] newInterval) {
+
+        // 병합된 interval 담는 list
+        List<int[]> modifyIntervals = new ArrayList<>();
+
+        int idx = 0;
+
+        // 병합 이전 구간
+        while (idx < intervals.length && intervals[idx][1] < newInterval[0]) {
+            modifyIntervals.add(intervals[idx]);
+            idx++;
+        }
+
+        // 병합이 필요한 구간 (newInterval과 겹치는 구간)
+        while (idx < intervals.length && intervals[idx][0] <= newInterval[1]) {
+            newInterval[0] = Math.min(intervals[idx][0], newInterval[0]);
+            newInterval[1] = Math.max(intervals[idx][1], newInterval[1]);
+            idx++;
+        }
+
+        // 최종 병합된 새로운 interval add        
+        modifyIntervals.add(newInterval);
+
+        // 병합 이후 구간
+        while (idx < intervals.length) {
+            modifyIntervals.add(intervals[idx]);
+            idx++;
+        }
+
+        return modifyIntervals.toArray(new int[modifyIntervals.size()][2]);
+    }
+}
+
diff --git a/kth-smallest-element-in-a-bst/Tessa1217.java b/kth-smallest-element-in-a-bst/Tessa1217.java
new file mode 100644
index 000000000..452fd995a
--- /dev/null
+++ b/kth-smallest-element-in-a-bst/Tessa1217.java
@@ -0,0 +1,51 @@
+/**
+ * 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 {
+
+    private int count = 0;
+
+    private int kthSmallValue = 0;
+
+    // 시간복잡도: O(k) (불균형 상태의 이진 트리일 경우 O(n))
+    public int kthSmallest(TreeNode root, int k) {
+        orderSearch(root, k);
+        return kthSmallValue;
+    }
+
+    // In Order Search
+    private void orderSearch(TreeNode node, int k) {
+
+        if (node == null) {
+            return;
+        }
+
+        // HINT => utilize the property of a BST => 좌측 리프 노드부터 탐색
+        orderSearch(node.left, k);
+
+        count++;
+
+        if (count == k) {
+            kthSmallValue = node.val;
+            return;
+        }
+
+        // search right side
+        orderSearch(node.right, k);
+
+    }
+
+}
+
diff --git a/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java b/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java
new file mode 100644
index 000000000..cc5d2dfb2
--- /dev/null
+++ b/lowest-common-ancestor-of-a-binary-search-tree/Tessa1217.java
@@ -0,0 +1,33 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+
+        if (root == null || root == p || root == q) {
+            return root;
+        }
+
+        // 재귀로 좌측과 우측 탐색
+        TreeNode left = lowestCommonAncestor(root.left, p, q);
+
+        TreeNode right = lowestCommonAncestor(root.right, p, q);
+
+        // 좌우 둘 다 null이 아니라면: 현재 root를 조상으로 하는 서브 트리에서 p와 q를 발견했음을 의미하므로 root가 공통 조상
+        if (left != null && right != null) {
+            return root;
+        } else if (left != null) {
+            return left;
+        } else {
+            return right;
+        }
+
+    }
+}
+
diff --git a/meeting-rooms-ii/Tessa1217.java b/meeting-rooms-ii/Tessa1217.java
new file mode 100644
index 000000000..2eda9e8df
--- /dev/null
+++ b/meeting-rooms-ii/Tessa1217.java
@@ -0,0 +1,55 @@
+import java.util.List;
+import java.util.PriorityQueue;
+
+/**
+ * Definition of Interval:
+ * public class Interval {
+ *     int start, end;
+ *     Interval(int start, int end) {
+ *         this.start = start;
+ *         this.end = end;
+ *     }
+ * }
+ */
+
+public class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: the minimum number of conference rooms required
+     */
+    // 시간복잡도: O(n log n)
+    public int minMeetingRooms(List<Interval> intervals) {
+
+        if (intervals == null || intervals.isEmpty()) {
+            return 0;
+        }
+
+        // 주어진 시간 인터벌 리스트를 시작 시간 기준으로 정렬
+        intervals.sort((i1, i2) -> i1.start - i2.start);
+
+        // PriorityQueue 선언: 시간 interval의 end time 기준
+        PriorityQueue<Interval> meetingRooms = new PriorityQueue<>((i1, i2) -> i1.end - i2.end);
+
+        for (Interval interval : intervals) {
+
+            // 최초 meeting room 
+            if (meetingRooms.isEmpty()) {
+                meetingRooms.offer(interval);
+                continue;
+            }
+
+            Interval meeting = meetingRooms.peek();
+            // (0, 8), (8, 10) is not conflict at 8
+            if (meeting.end <= interval.start) {
+                // 앞의 회의 종료되었으므로 회의실 재사용
+                meetingRooms.poll();
+            }
+            // 새 회의실 추가
+            meetingRooms.offer(interval);
+        }
+
+        return meetingRooms.size();
+
+    }
+}
+
diff --git a/meeting-rooms/Tessa1217.java b/meeting-rooms/Tessa1217.java
new file mode 100644
index 000000000..3ad8cf994
--- /dev/null
+++ b/meeting-rooms/Tessa1217.java
@@ -0,0 +1,42 @@
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Definition of Interval:
+ * public class Interval {
+ *     int start, end;
+ *     Interval(int start, int end) {
+ *         this.start = start;
+ *         this.end = end;
+ *     }
+ * }
+ */
+
+public class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: if a person could attend all meetings
+     */
+
+    // 시간복잡도: O(n log n) - 정렬, 공간복잡도: O(1)
+    public boolean canAttendMeetings(List<Interval> intervals) {
+        // Write your code here
+
+        if (intervals == null || intervals.isEmpty()) return true;
+
+        Collections.sort(intervals, (i1, i2) -> i1.start - i2.start);
+
+        Interval previous = intervals.get(0);
+
+        for (int i = 1; i < intervals.size(); i++) {
+            Interval current = intervals.get(i);
+            if (previous.end > current.start) {
+                return false;
+            }
+            previous = current;
+        }
+
+        return true;
+    }
+}
+
diff --git a/word-search-ii/Tessa1217.java b/word-search-ii/Tessa1217.java
new file mode 100644
index 000000000..6e4e51a87
--- /dev/null
+++ b/word-search-ii/Tessa1217.java
@@ -0,0 +1,90 @@
+import java.util.ArrayList;
+import java.util.List;
+
+class Solution {
+
+    private int[] dx = {0, 0, 1, -1};
+    private int[] dy = {1, -1, 0, 0};
+
+    private int m;
+    private int n;
+
+    class TrieNode {
+        // 단어는 영어 소문자만으로 이루어짐
+        TrieNode[] nodes = new TrieNode[26];
+        String word = null;
+    }
+
+    private void insert(TrieNode root, String word) {
+        TrieNode node = root;
+        for (char c : word.toCharArray()) {
+            int idx = c - 'a';
+            if (node.nodes[idx] == null) {
+                node.nodes[idx] = new TrieNode();
+            }
+            node = node.nodes[idx];
+        }
+        // 단어
+        node.word = word;
+    }
+
+    public List<String> findWords(char[][] board, String[] words) {
+
+        List<String> existingWords = new ArrayList<>();
+
+        // 탐색 최적화를 위해 TrieNode 생성
+        TrieNode root = new TrieNode();
+        for (String word : words) {
+            insert(root, word);
+        }
+
+        m = board.length;
+        n = board[0].length;
+
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                dfs(board, i, j, root, existingWords);
+            }
+        }
+
+        return existingWords;
+    }
+
+    private void dfs(char[][] board, int i, int j, TrieNode node, List<String> existingWords) {
+
+        char c = board[i][j];
+
+        // 방문 처리 되었거나 TrieNode에 없는 글자라면 탐색 X => Pruning
+        if (c == '#' || node.nodes[c - 'a'] == null) {
+            return;
+        }
+
+        node = node.nodes[c - 'a'];
+
+        // node의 완성된 단어가 있다면
+        if (node.word != null) {
+            existingWords.add(node.word);
+            node.word = null;
+        }
+
+        // 방문 처리
+        board[i][j] = '#';
+
+        for (int idx = 0; idx < 4; idx++) {
+            int ni = i + dx[idx];
+            int nj = j + dy[idx];
+            if (isRange(ni, nj)) {
+                dfs(board, ni, nj, node, existingWords);
+            }
+        }
+
+        board[i][j] = c;
+    }
+
+    // 탐색 범위 조건
+    private boolean isRange(int i, int j) {
+        return i >= 0 && j >= 0 && i < m && j < n;
+    }
+
+}
+