func mergeSort(nums []int) []int {
     length := len(nums)
     if length < 2 {
         return nums
     }
     middle := length / 2
     left := nums[0:middle]
     right := nums[middle:]
     return merge(mergeSort(left), mergeSort(right))
 }

 func merge(left []int, right []int) []int {
     var result []int
     for len(left) != 0 && len(right) != 0 {
         if left[0] <= right[0] {
             result = append(result, left[0])
             left = left[1:]
         } else {
             result = append(result, right[0])
             right = right[1:]
         }
     }
     //fmt.Println(left,right)
     for len(left) != 0 {
         result = append(result, left[0])
         left = left[1:]
     }

     for len(right) != 0 {
         result = append(result, right[0])
         right = right[1:]
     }

     return result
 }