Problem URL: Count good meals

We will use a hashmap to solve this problem. We will iterate over the deliciousness array and for each element, we will check if the element is a power of two. If it is, we will add the element to the hashmap. If it is not, we will check if the element is a power of two minus the element in the hashmap. If it is, we will add the element to the hashmap. We will return the result.

class Solution:
    def countPairs(self, deliciousness: List[int]) -> int:
        count = collections.Counter()
        res = 0
        for d in deliciousness:
            for i in range(22):
                res += count[2**i - d]
            count[d] += 1
        return res % (10**9+7)

Time complexity: O(nlog(n))
Space complexity: O(n)