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;
+	}
+}
+