diff --git a/contains-duplicate/essaysir.java b/contains-duplicate/essaysir.java
new file mode 100644
index 0000000000..02fa34b6dc
--- /dev/null
+++ b/contains-duplicate/essaysir.java
@@ -0,0 +1,12 @@
+import java.util.*;
+
+class Solution {
+	public boolean containsDuplicate(int[] nums) {
+		Set<Integer> sets = new HashSet<>();
+		for ( int i = 0; i < nums.length; i++){
+			boolean added = sets.add(nums[i]);
+			if (!added) return true;
+		}
+		return false;
+	}
+}
\ No newline at end of file
diff --git a/two-sum/essaysir.java b/two-sum/essaysir.java
new file mode 100644
index 0000000000..2476360f7e
--- /dev/null
+++ b/two-sum/essaysir.java
@@ -0,0 +1,17 @@
+import java.util.*;
+
+class Solution {
+	public int[] twoSum(int[] nums, int target) {
+		// TWO Sum , 순서는 상관이 없음. NC2 를 계산 필요
+		int[] result = new int[2];
+		for ( int i = 0; i < nums.length; i++){
+			for ( int j = i + 1; j < nums.length; j++){
+				if ( target == nums[i] + nums[j]){
+					result[0] = i;
+					result[1] = j;
+				}
+			}
+		}
+		return result;
+	}
+}
\ No newline at end of file