Leetcode：汇总区间

输入：nums = [0,1,2,4,5,7]
输出：["0->2","4->5","7"]
解释：区间范围是：
[0,2] --> "0->2"
[4,5] --> "4->5"
[7,7] --> "7"

输入：nums = [0,2,3,4,6,8,9]
输出：["0","2->4","6","8->9"]
解释：区间范围是：
[0,0] --> "0"
[2,4] --> "2->4"
[6,6] --> "6"
[8,9] --> "8->9"

输入：nums = []
输出：[]

0 <= nums.length <= 20
-231 <= nums[i] <= 231 - 1
nums 中的所有值都 互不相同
nums 按升序排列

List<String> result = new ArrayList<>();
        if (null == nums || nums.length ==0) {
            return result;
        } else if (nums.length == 1) {
            result.add(String.valueOf(nums[0]));
            return result;
        }
        int start = nums[0];
        int end = nums[0];
        for (int i=1;i<nums.length;i++) {
            if (nums[i] - nums[i-1] == 1) {
                end = i == nums.length-1 ? nums[i] : end;
                continue;
            }
            result.add(start == nums[i-1]? String.valueOf(start) : start + "->" + nums[i - 1] );
            start = nums[i];
            if (i>=nums.length-1) {
                result.add(start+"");
            }
        }
        if (start<end) {
            result.add(start + "->" + end);
        }
        return result;

public List<String> summaryRanges(int[] nums) {
        List<String> target = new ArrayList<>();
        if(nums.length == 0) return target;
        StringBuilder sb = new StringBuilder();
        for (int i = 0 ,j = i + 1;j < nums.length; i++,j++) {
            if(nums[j] - 1 > nums[i]) {
                sb.append(nums[i]);
                target.add(sb.toString());
                sb = new StringBuilder();
            }else {
                if(sb.length() == 0) {
                    sb.append(nums[i]);
                    sb.append("->");
                }
            }
        }
        target.add(sb.append(nums[nums.length - 1]).toString());
        return target;
    }