1711

class Solution {
public:
    int countPairs(vector<int>& deliciousness) {
        unordered_map<int, int> counter;

        long long ans=0, mod=int(1e9)+7;
        for(int d: deliciousness){
            for(int i=1, sum=1; i<=22; i++, sum*=2)
                if(counter.count(sum-d))
                    ans = (ans + counter[sum-d])%mod;
            counter[d]++;
        }
        return ans;
    }
};