Untitled

import java.util.*;

public class Main {
    static class Solution {
        public int countPairs(int[] deliciousness) {
            final int MOD = 1_000_000_007;
            Map<Integer, Integer> freq = new HashMap<>();
            long ans = 0;

            // 2^21 = 2097152, safe enough for common constraints
            for (int val : deliciousness) {
                int power = 1;

                for (int i = 0; i <= 21; i++) {
                    int needed = power - val;
                    ans = (ans + freq.getOrDefault(needed, 0)) % MOD;
                    power <<= 1;
                }

                freq.put(val, freq.getOrDefault(val, 0) + 1);
            }

            return (int) ans;
        }
    }

    public static void main(String[] args) {
        Solution sol = new Solution();

        int[] deliciousness = {1, 3, 5, 7, 9};
        System.out.println(sol.countPairs(deliciousness)); // Output: 4
    }
}