Count Good Meals LeetCode solution in C++

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class Solution {
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 public:
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  int countPairs(vector<int> &deliciousness) {
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    int cnt = 0;
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    unordered_map<int, int> mp;
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    mp[deliciousness[0]]++;
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    int mod = 1e9 + 7;
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    for (int i = 1; i < deliciousness.size(); i++) {
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      for (int p = 1; p <= (1 << 21); p *= 2) {
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        if (mp.find(p - deliciousness[i]) != mp.end()) {
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          cnt = (cnt + mp[p - deliciousness[i]]) % mod;
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        }
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      }
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      mp[deliciousness[i]]++;
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    }
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    return cnt % mod;
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  }
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};