Series: #groupelements – seperate a list into several groups

// https://code.dennyzhang.com/summary-ranges
// Basic Ideas: twopointer + simulation
//
// Complexity: Time O(n), Space O(1)
func summaryRanges(nums []int) []string {
    res := []string{}
    // nums[i...j]
    i := 0
    for j:=0; j<len(nums); j++ {
        if j+1<len(nums) && nums[j]+1 == nums[j+1] {
            continue
        }
       // last group or group ends
        if i==j {
            res = append(res, fmt.Sprintf("%d", nums[i]))
        } else {
            res = append(res, fmt.Sprintf("%d->%d", nums[i], nums[j]))
        }
        // need to start a new group
        i = j+1
    }
    return res
}