Leetcode-Missing Ranges

Given a sorted integer array where the range of elements are [lower, upper] inclusive, return its missing ranges.

For example, given [0, 1, 3, 50, 75], lower = 0 and upper = 99, return ["2", "4->49", "51->74", "76->99"].

A better solution:

public class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<String> resList = new LinkedList<String>();
        if (nums.length==0){
            addRange(resList,lower,upper);
            return resList;
        }
        
        int first = -1;
        for (int i=0;i<nums.length;i++)
            if (nums[i]>=lower){
                first = i;
                break;
            }
        int start = nums[first], end = nums[first];
        addRange(resList,lower,start-1);
        for (int i=first+1;i<nums.length;i++){
            if (nums[i]>upper) break;
            
            if (nums[i]==end+1){
                end = nums[i];
            } else {
                addRange(resList,end+1,nums[i]-1);
                start = nums[i];
                end = nums[i];
            }
        }
        addRange(resList,end+1,upper);
        return resList;
    }
    
    public void addRange(List<String> resList, int lower, int upper){
        if (upper < lower) return;
        
        if (lower==upper) resList.add(Integer.toString(lower));
        else resList.add(Integer.toString(lower)+"->"+Integer.toString(upper));
    }
}

Solution:

 1 public class Solution {
 2     public List<String> findMissingRanges(int[] A, int lower, int upper) {
 3         //for a range lower-upper, and a number A[i], we have conditions:
 4         //1. A[i]<lower: move to i+1;
 5         //2. A[i]==lower: lower -> A[i]+1
 6         //3. lower<A[i]<=upper: generate a range: lower->A[i]-1; lower becomes A[i]+1. NOTE A[i]==upper: end of the program.
 7         //4. A[i]>upper: get range: lower->upper, end of the problem.
 8 
 9         List<String> res = new ArrayList<String>();
10 
11         for (int i=0;i<A.length;i++){
12             if (A[i]<lower) continue;
13            
14             if (A[i]==lower){
15                 lower=A[i]+1;
16                 continue;
17             }
18 
19             if (A[i]>lower && A[i]<=upper){
20                 String range = "";
21                 if (lower!=A[i]-1) range = Integer.toString(lower)+"->"+Integer.toString(A[i]-1);
22                 else range = Integer.toString(lower);
23                 res.add(range);
24                 lower = A[i]+1;
25                 if (A[i]==upper) break;
26                 else continue;
27             }
28 
29             if (A[i]>upper){
30                 String range = "";
31                 if (lower!=upper) range = Integer.toString(lower)+"->"+Integer.toString(upper);
32                 else range = Integer.toString(lower);
33                 res.add(range);
34                 lower = A[i]+1;
35                 break;
36             }
37         }
38 
39         if (lower<=upper){
40             String range = "";
41             if (lower!=upper) range = Integer.toString(lower)+"->"+Integer.toString(upper);
42             else range = Integer.toString(lower);
43             res.add(range);
44         }
45 
46         return res;
47     }
48 }