feat: add scala solution for 1. two sum

scala/1-Two-Sum.scala

@@ -0,0 +1,34 @@
+import scala.collection.mutable
+
+object Solution {
+  def twoSum(nums: Array[Int], target: Int): Array[Int] = {
+    val numsWithIndex = nums.zipWithIndex
+    val targets = numsWithIndex.toMap
+
+    def compliment(v: Int): Option[Int] = targets.get(target - v)
+
+    numsWithIndex
+      .find { case (v, i) => !compliment(v).forall(_ == i) }
+      .map { case (v, i) => Array(i, compliment(v).get) }
+      .orNull
+  }
+
+  /**
+   * Optimization of above solution to do it in "one pass"
+   * i.e. build the map as we traverse the input collection
+   */
+  def twoSumOnePass(nums: Array[Int], target: Int): Array[Int] = {
+    val targets = mutable.Map[Int, Int]()
+
+    for ((v, i) <- nums.zipWithIndex) {
+      val answer = targets.get(target - v).map(Array(_, i))
+
+      if (answer.nonEmpty)
+        return answer.get
+
+      targets.put(v, i)
+    }
+
+    null
+  }
+}