add twosum solution

Author: ErdemOzgen

go/1-Two-Sum.go

@@ -0,0 +1,12 @@
+package main
+
+func twoSum(nums []int, target int) []int {
+	prevMap := make(map[int]int)
+	for i, num := range nums {
+		if j, ok := prevMap[target-num]; ok {
+			return []int{j, i}
+		}
+		prevMap[num] = i
+	}
+	return []int{}
+}