func summaryRanges(nums []int) []string {
n := len(nums)
list := []string{}
for i:=0; i < n; i++{
left := i
for ;i<n-1 && nums[i]+1==nums[i+1] ;i++{
}
str := strconv.Itoa(nums[left])
if left < i {
str += "->"
str += strconv.Itoa(nums[i])
}
list = append(list, str)
}
return list
}