feat: Add Java solutions for competitive programming problems

Java/leetcode/easy/TwoSum.java

@@ -0,0 +1,35 @@
+/**
+ * Leetcode #1 - Two Sum
+ * Problem: Given an array of integers, return indices of the two numbers 
+ * such that they add up to a specific target.
+ * 
+ * Approach: Using HashMap to store number and its index
+ * Time Complexity: O(n)
+ * Space Complexity: O(n)
+ */
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class TwoSum {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            int complement = target - nums[i];
+            if (map.containsKey(complement)) {
+                return new int[] { map.get(complement), i };
+            }
+            map.put(nums[i], i);
+        }
+        return new int[] {};
+    }
+
+    // Main method for testing
+    public static void main(String[] args) {
+        TwoSum solution = new TwoSum();
+        int[] nums = {2, 7, 11, 15};
+        int target = 9;
+        int[] result = solution.twoSum(nums, target);
+        System.out.println("Indices: " + result[0] + ", " + result[1]);
+    }
+}