# 1711. Count Good Meals
###### tags: `Leetcode` `Medium` `Two Sum`
Link: https://leetcode.com/problems/count-good-meals/description/
## 思路
典型two sum
target sum是从$1$到$2^{22}$所有2的次方数
## Code

class Solution {
    public int countPairs(int[] deliciousness) {
        Map<Integer, Integer> map = new HashMap<>();
        int ans = 0, mod = (int)1e9+7;
        for(int d:deliciousness){
            int pow = 1;
            for(int i=0; i<22; i++){
                ans = (ans+map.getOrDefault(pow-d, 0))%mod;
                pow*=2;
            }
            map.put(d, map.getOrDefault(d, 0)+1);
        }
        return ans;
    }
}