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

<p>You can pick <strong>any</strong> two different foods to make a good meal.</p>

<p>Given an array of integers <code>deliciousness</code> where <code>deliciousness[i]</code> is the deliciousness of the <code>i<sup>​​​​​​th</sup>​​​​</code>​​​​ item of food, return <em>the number of different <strong>good meals</strong> you can make from this list modulo</em> <code>10<sup>9</sup> + 7</code>.</p>

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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> deliciousness = [1,3,5,7,9]
<strong>Output:</strong> 4
<strong>Explanation: </strong>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.
</pre>

<p><strong class="example">Example 2:</strong></p>

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

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= deliciousness.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= deliciousness[i] &lt;= 2<sup>20</sup></code></li>
</ul>

class Solution {
public:
    int countPairs(vector<int>& deliciousness) {
        sort(deliciousness.begin(), deliciousness.end());
        int ans = 0;
        unordered_map<int, int> um;
        int mod = 1e9 + 7;
        for(int i=0; i < deliciousness.size(); i++){
            if(um.find(deliciousness[i]) != um.end()){
                ans += (um[deliciousness[i]] % mod);
                ans %= mod;
            }

            for(int k=0; k <= 25; k++){
                int power = (1 << k);
                if (power > deliciousness[i]){ 
                    int num = power - deliciousness[i];
                    um[num]++;
                }
                // cout<<num<<"-->";
                // if((sum & (1 << k)) > 0){
                //     number_of_once++;
                // }
                // if(number_of_once > 1) break;
            }
        }
        // for(int i=0; i < deliciousness.size(); i++){
        //     for(int j = i+1; j< deliciousness.size(); j++){
        //         int sum = deliciousness[i] + deliciousness[j];
        //         int number_of_once = 0;
                // for(int k=0; k <= 31; k++){
                //     if((sum & (1 << k)) > 0){
                //         number_of_once++;
                //     }
                //     if(number_of_once > 1) break;
                // }
        //         if(number_of_once == 1){
        //             ans++;
        //         }
        //     }
        // }
        return ans;
    }
};

// 1000
// 0100
// 0010
// 0001
144256