add 'Single Number'

tags/hash-table/singleNumber/main.go

@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+
+func main() {
+	var nums []int
+
+	nums = []int{2, 1, 2}
+	fmt.Println(singleNumber(nums))
+
+	nums = []int{2, 1, 2, 1, 4}
+	fmt.Println(singleNumber(nums))
+}
+
+func singleNumber(nums []int) int {
+	var ans int
+	for i := 0; i < len(nums); i++ {
+		ans ^= nums[i]
+	}
+	return ans
+}