added optimised twoSum solution

src/main/kotlin/math/TwoSum.kt

@@ -24,3 +24,37 @@ fun twoSum(nums: IntArray, target: Int): IntArray{
  return intArrayOf(0,1)
 
 }
+
+/**
+ * Approach 2: Using HashMap
+ *
+ * Complexity Analysis:
+ *
+ * Time complexity: O(n)
+ * Space complexity: O(n)
+ *
+ * Create an empty mutableMap and for every num in nums
+ * if map contains target-num, return num and target-num,
+ * otherwise add num, this approach returns all distinct pairs
+ * of such pairs.
+ * @param nums Array of integers.
+ * @param target Integer target.
+ * @return the two numbers such that they add up to target.
+ */
+fun twoSumOptimised(nums: IntArray, target: Int): Array<Pair<Int, Int>>{
+
+ val array: MutableList<Pair<Int, Int>> = mutableListOf()
+ val map: MutableMap<Int, Int> = HashMap()
+ for(num in nums) {
+ val targetDiff = target - num;
+ if(map[targetDiff] == null)
+ map[num] = 1
+ else {
+ array.add(Pair(targetDiff, num))
+ }
+ }
+
+ return array.toTypedArray()
+
+
+}

src/test/kotlin/math/TwoSum.kt

@@ -12,4 +12,14 @@ class TwoSumTest {
  val result = intArrayOf(0,1)
  assert(twoSum(array,target).contentEquals(result))
  }
+
+ @Test
+ fun testTwoSumOptimised(){
+ val array = intArrayOf(1, 0, -1, 2, 4, 5, 3, 2)
+ val target: Int = 4
+ val result = twoSumOptimised(array, target).apply {
+ this.all { it.first + it.second == target }
+ }
+ assert(result.isNotEmpty())
+ }
 }