diff --git a/merge-two-sorted-lists/donghyeon95.java b/merge-two-sorted-lists/donghyeon95.java
new file mode 100644
index 000000000..e4f43c128
--- /dev/null
+++ b/merge-two-sorted-lists/donghyeon95.java
@@ -0,0 +1,37 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+	public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
+		// O(N)
+		// 2포인터로 지나가용 하면 되는 문제
+		ListNode result = new ListNode();
+		ListNode nowNode = result;
+
+
+		while (list1!=null || list2!=null) {
+			int first = list1==null? 101: list1.val;
+			int second = list2==null? 101: list2.val;
+
+			if (first < second) {
+				nowNode.next = new ListNode(first);
+				nowNode = nowNode.next;
+				list1 = list1.next;
+			} else {
+				nowNode.next = new ListNode(second);
+				nowNode = nowNode.next;
+				list2 = list2.next;
+			}
+		}
+
+		return result.next;
+	}
+}
+
diff --git a/missing-number/donghyeon95.java b/missing-number/donghyeon95.java
new file mode 100644
index 000000000..03985af52
--- /dev/null
+++ b/missing-number/donghyeon95.java
@@ -0,0 +1,19 @@
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+// O(N)
+class Solution {
+	public int missingNumber(int[] nums) {
+		Set<Integer> numSet = Arrays.stream(nums).boxed().collect(Collectors.toSet());
+
+		for (int i=0; i<nums.length; i++) {
+			if (!numSet.contains(i)) return i;
+		}
+
+		return nums.length;
+	}
+}
+