163. 缺失的区间 仅ac代码+注释

class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<String> ans = new ArrayList<String>();
        String tp = "";
        int len = nums.length;
        //处理空
        if(len == 0){
            ans.add(Add(lower-1,upper+1));
            return ans;
        }
        //处理开头
        if(lower < nums[0]){
            ans.add(Add( lower-1 ,nums[0])) ;
        }
        for(int i=0;i<len-1;++i){
            if(nums[i]+1!=nums[i+1]){
                ans.add(Add(nums[i],nums[i+1]));
            }

        }
        //处理结尾
        if(nums[len-1]<upper){
            ans.add(Add(nums[len-1],upper+1));
        }
        return ans;
    }
    public String Add(int l,int r){
        String fin = "";
        if(l+2 == r){
            fin = String.valueOf(l+1);
        }
        else{
            fin = String.valueOf(l+1) + "->" + String.valueOf(r-1);
        }
        return fin;
    }
}