1711 Count Good Meals

A good meal is a meal that contains exactly two different food items with a sum of deliciousness equal to a power of two.

You can pick any two different foods to make a good meal.

Given an array of integers deliciousness where deliciousness[i] is the deliciousness of the ith item of food, return the number of different good meals you can make from this list modulo 109 + 7.

Note that items with different indices are considered different even if they have the same deliciousness value.

Example 1:

Input: deliciousness = [1,3,5,7,9]
Output: 4
Explanation: The good meals are (1,3), (1,7), (3,5) and, (7,9).
Their respective sums are 4, 8, 8, and 16, all of which are powers of 2.

Example 2:

Input: deliciousness = [1,1,1,3,3,3,7]
Output: 15
Explanation: The good meals are (1,1) with 3 ways, (1,3) with 9 ways, and (1,7) with 3 ways.

Solution

class Solution {
    int mod = (int) 1e9 + 7; //Math.pow(10,9) + 7;
    public int countPairs(int[] deliciousness) {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();

        int result = 0;
        for (int i = 0; i < deliciousness.length; i++){
            int power = 1;
            for (int j = 0; j < 22; j++){
                if (map.containsKey(power - deliciousness[i])){
                    result = result + map.get(power - deliciousness[i]);
                    result = result % mod;
                  /*
                  Given an array of integers `deliciousness` where `deliciousness[i]` is the deliciousness of the `ith` item of food, return *the number of different **good meals** you can make from this list modulo* `109 + 7`.
                  */
                }
                power = power * 2;
            }

            map.put(deliciousness[i], map.getOrDefault(deliciousness[i],0) + 1);

        }
        return result;

    }
}

// TC: O(22n) = O(n)
// SC: O(n)