upd

1. Two Sum/Solution.java

@@ -0,0 +1,35 @@
+import java.util.Arrays;
+import java.util.HashMap;
+
+class Solution {
+    public static void main(String[] args) {
+      int[] test1 = {2, 7, 11, 15}; int target1 = 9;
+      int[] test2 = {3, 2, 4}; int target2 = 6;
+      int[] test3 = {3, 3}; int target3 = 6;
+
+
+      System.out.println("twoSum( " + Arrays.toString(test1) + ", " + target1 + " ): " + Arrays.toString(twoSum(test1, target1)));
+      System.out.println("twoSum( " + Arrays.toString(test2) + ", " + target2 + " ): " + Arrays.toString(twoSum(test2, target2)));
+      System.out.println("twoSum( " + Arrays.toString(test3) + ", " + target3 + " ): " + Arrays.toString(twoSum(test3, target3)));
+
+    }
+
+    static int[] twoSum(int[] nums, int target) {
+        int[] res = new int[2];
+
+        HashMap<Integer, Integer> d = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+          var remainderIdx = d.get(target - nums[i]);
+          if (remainderIdx != null) {
+            res[0] = i;
+            res[1] = remainderIdx;
+            return res;
+          } else {
+            d.put(nums[i], i);
+          }
+        }
+        
+        return res;
+    }
+}