Given a sorted integer array without duplicates, return the summary of its ranges.

For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].

public class Solution {
    public List<String> summaryRanges(int[] nums) {
        LinkedList<String> list = new LinkedList<String>();
        //若为null则返回null
        if(nums==null){
            return null;
        }
        //用来遍历的指针i
        int i = 0;
        int len = nums.length;
        //StringBuffer用来存储字符串
        StringBuffer sb = new StringBuffer();
        while(i<len){
            //连续数字起始位置
            int begin = i;
            while(i+1<len&&(nums[i+1]==nums[i]+1)){
                i++;
            }
            //连续数字终止位置
            int end = i++;
            if(begin==end){
                list.add(String.valueOf(nums[begin]));
            }
            else{
                sb.append(nums[begin]);
                sb.append("->");
                sb.append(nums[end]);
                list.add(sb.toString());
                sb.delete(0, sb.length());
            }
        }
        return list;
    }
}

Given a sorted integer array without duplicates, return the summary of its ranges.

For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].