LeetCode/problems/number-of-matching-subsequences.cpp

class Solution {
    bool matches(const string& s, const string& word) const
    {
        auto s_i = 0;

        for (auto i = 0; s_i < s.size() && i < word.size(); i++) {
            if (s[s_i] == word[i]) {
                s_i++;
            }
        }

        return s_i == s.size();
    }

    map<string, int> preprocess(const vector<string>& words) const
    {
        map<string, int> histogram;

        for (auto& w : words) {
            histogram[w]++;
        }

        return histogram;
    }

public:
    int numMatchingSubseq(string s, vector<string>& words)
    {
        auto histogram = preprocess(words);
        return accumulate(histogram.begin(), histogram.end(), 0, [&](int acc, const auto& pair) {
            return acc + (matches(pair.first, s) ? pair.second : 0);
        });
    }
};