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:

public class Solution {
    public List<String> findMissingRanges(int[] A, int lower, int upper) {
        //for a range lower-upper, and a number A[i], we have conditions:
        //1. A[i]<lower: move to i+1;
        //2. A[i]==lower: lower -> A[i]+1
        //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.
        //4. A[i]>upper: get range: lower->upper, end of the problem.

        List<String> res = new ArrayList<String>();

        for (int i=0;i<A.length;i++){
            if (A[i]<lower) continue;
           
            if (A[i]==lower){
                lower=A[i]+1;
                continue;
            }

            if (A[i]>lower && A[i]<=upper){
                String range = "";
                if (lower!=A[i]-1) range = Integer.toString(lower)+"->"+Integer.toString(A[i]-1);
                else range = Integer.toString(lower);
                res.add(range);
                lower = A[i]+1;
                if (A[i]==upper) break;
                else continue;
            }

            if (A[i]>upper){
                String range = "";
                if (lower!=upper) range = Integer.toString(lower)+"->"+Integer.toString(upper);
                else range = Integer.toString(lower);
                res.add(range);
                lower = A[i]+1;
                break;
            }
        }

        if (lower<=upper){
            String range = "";
            if (lower!=upper) range = Integer.toString(lower)+"->"+Integer.toString(upper);
            else range = Integer.toString(lower);
            res.add(range);
        }

        return res;
    }
}