Two-Letter Card Game — C++

// Time:  O(n + 26)
// Space: O(26)

// freq table, math
class Solution {
public:
    int score(vector<string>& cards, char x) {
        vector<int> cnt1(10), cnt2(10);
        int cnt3 = 0;
        for (const auto& s : cards) {
            if (s.find(x) == string::npos) {
                continue;
            }
            if (s[0] == x && s[1] == x) {
                ++cnt3;
            } else if (s[0] == x) {
                ++cnt1[s[1] - 'a'];
            } else if (s[1] == x) {
                ++cnt2[s[0] - 'a'];
            }
        }
        const int total1 = accumulate(cbegin(cnt1), cend(cnt1), 0);
        const int total2 = accumulate(cbegin(cnt2), cend(cnt2), 0);
        const int mx1 = ranges::max(cnt1);
        const int mx2 = ranges::max(cnt2);
        const int pair1 = min(total1 - mx1, total1 / 2);
        const int pair2 = min(total2 - mx2, total2 / 2);
        const int pair3 = min((total1 - 2 * pair1) + (total2 - 2 * pair2), cnt3);
        return (pair1 + pair2) + pair3 + min(pair1 + pair2, (cnt3 - pair3) / 2);
    }
};