min(set)+max(set) < target Freq:high

https://lina.bitcron.com/post/code/2018-summer-fb-intern-mian-jing

类似 3 sum smaller(fixed one side and move the other side and then pick any elems from that range).O(n)可解2sum + subsets结合的一题，给一个int array 没有重复 和一个target，要求数可以生成的subset数目满足条件 min(subset) + max(subset) < target

input: sorted array, int targetoutput: # of subsets

    public int numOfSubsets(int nums[], int target){
        int i = 0, j = nums.length-1;
        int res = 0;
        while(i<=j){
            if(nums[i]+nums[j]>=target){
                j--;
            }
            else{
            res += Math.pow(2,(j-i));
            i++;
            }
        }
        return res;
    }