C++ auto

Jimmy (xiaoke) Shen

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Jan 3, 2021

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Auto used for map

1711. Count Good Meals

const int MOD = 1e9 + 7;
class Solution {
public:
    int countPairs(vector<int>& a) {
        map<int, int> cnt;
        for (auto &x : a) cnt[x]++;
        int k2;
        int ret = 0;
        for (auto &[k1, v] : cnt) {
            for (int sum = 1; sum <= (1 << 21); sum <<= 1) {
                k2 = sum - k1;
                if (k2 < k1) continue;
                if (cnt.find(k2) == cnt.end()) continue;
                if (k1 == k2) {
                    ret += (1ll * v * (v - 1) / 2) % MOD;
                } else {
                    ret += v * cnt[k2] % MOD;
                }
                
                if (ret >= MOD) ret %= MOD;
            }
        }
        return ret;
    }
};