228. Summary Ranges

Your input

[0,1,2,4,5,7]

Your answer

["0->1->2","4->5"]

Expected answer

["0->2","4->5","7"]

Input:[0,2,3,4,6,8,9]

Output:["0->0","2->4","6->6","8"]

Expected:["0","2->4","6","8->9"]

50.15 %

// LC228 Beats 50.15 %
// There are 2 edge cases:
// 1.start == end like "6->6" should be treated as a single number "6"， so we should check prev != start
// 2. Since discontinuous gap triggers adding String to result, the last String won't be added. We should deal with it before return
class Solution {
    public List<String> summaryRanges(int[] nums) {
        List<String> result = new ArrayList<>();
        if (nums == null || nums.length <= 0) return result;
        int prev = nums[0];
        int start = prev;
        StringBuilder sb = new StringBuilder();
        sb.append(start);
        for (int i = 1; i < nums.length; i++) {
            if (nums[i] != prev + 1) {
                if (start != prev) sb.append("->" + prev);
                result.add(sb.toString()); // add previous String to result
                sb.setLength(0); // clear StringBuilder
                start = nums[i];
                sb.append(start); // new Starting point
            }
            prev = nums[i];
        }
        if (sb.length() != 0) {
            if (start != prev) sb.append("->" + prev);
            result.add(sb.toString());
        }
        return result;
    }
}