Added

'Two Sum'

Author: anthonyzhub

Two Sum.java

@@ -0,0 +1,56 @@
+// https://leetcode.com/problems/two-sum/
+
+class Solution {
+    public int[] twoSum1(int[] nums, int target) {
+
+        /* BRUTE FORCE */
+        
+        // Create a return list
+        int[] ans = new int[2];
+
+        // Iterate nums
+        for (int i = 0; i < nums.length; i++) {
+            for (int j = i + 1; j < nums.length; j++) {
+                if (nums[i] + nums[j] == target) {
+                    ans[0] = i;
+                    ans[1] = j;
+
+                    return ans;
+                }
+            }
+        }
+
+        return ans;
+    }
+
+    public int[] twoSum(int[] nums, int target) {
+        
+        /* HASH MAP APPROACH 
+         * 
+         * Time Complexity: O(n) = n is the length of nums. 
+         * 
+         * Space Complexity: O(n) = n is map size.
+        */
+
+        // Create a hash map
+        Map<Integer, Integer> map = new HashMap<>();
+
+        // Put all the elements to hash map
+        for (int i = 0; i < nums.length; i++) {
+            map.put(nums[i], i);
+        }
+
+        // Find the complement
+        // I.e., nums[i] + X = target. X is the complement.
+        for (int i = 0; i < nums.length; i++) {
+            int complement = target - nums[i];
+
+            // If complement exist in map and it isn't itself, then return list
+            if (map.containsKey(complement) && map.get(complement) != i) {
+                return new int[] {map.get(complement), i};
+            }
+        }
+        
+        return null;
+    }
+}