Missing Ranges 解答

 1 public class Solution {
 2     public List<String> findMissingRanges(int[] nums, int lower, int upper) {
 3         List<String> result = new ArrayList<>();
 4         if (nums == null || nums.length == 0) {
 5             addRange(result, lower, upper);
 6             return result;
 7         }
 8         int len = nums.length;
 9         // process head
10         if (nums[0] > lower) {
11             addRange(result, lower, nums[0] - 1);
12         }
13         for (int i = 1; i < len; i++) {
14             if (nums[i] > nums[i - 1] + 1) {
15                 addRange(result, nums[i - 1] + 1, nums[i] - 1);
16             }
17         }
18         // process tail
19         if (nums[len - 1] < upper) {
20             addRange(result, nums[len - 1] + 1, upper);
21         }
22         return result;
23     }
24     
25     private void addRange(List<String> result, int low, int high) {
26         StringBuilder sb = new StringBuilder();
27         sb.append(low);
28         if (high > low) {
29             sb.append("->");
30             sb.append(high);
31         }
32         result.add(sb.toString());
33     }
34 }