2568. Minimum Impossible OR

You are given a 0-indexed integer array nums.

We say that an integer x is expressible from nums if there exist some integers 0 <= index1 < index2 < … < indexk < nums.length for which nums[index1] | nums[index2] | … | nums[indexk] = x. In other words, an integer is expressible if it can be written as the bitwise OR of some subsequence of nums.

Return the minimum positive non-zero integer that is not expressible from nums.

class Solution {
public:
    int minImpossibleOR(vector<int>& A) {
        unordered_set<int> us(begin(A), end(A));
        for(long long i = 0; ; i++) {
            long long l = 1<<i;
            if(!us.count(l)) return l;
        }
        return -1;
    }
};