Maximum Score Words Formed by Letters — C++

// Time:  O(n * 2^n)
// Space: O(n)

class Solution {
public:
    int maxScoreWords(vector<string>& words, vector<char>& letters, vector<int>& score) {
        unordered_map<char, int> letter_count;
        vector<unordered_map<char, int>> word_counts(words.size());
        vector<int> word_scores(words.size());
        for (const auto& c : letters) {
            ++letter_count[c];
        }
        for (int i = 0; i < words.size(); ++i) {
            for (const auto& c : words[i]) {
                ++word_counts[i][c];
                word_scores[i] += score[c - 'a'];
            }
        }
        int result = 0;
        backtracking(words, word_scores, word_counts, 0, 0, &letter_count, &result);
        return result;
    }

private:
    void backtracking(const vector<string>& words,
                      const vector<int>& word_scores,
                      const vector<unordered_map<char, int>>& word_counts,
                      int curr,
                      int curr_score,
                      unordered_map<char, int> *letter_count,
                      int *result) {
        *result = max(*result, curr_score);
        for (int i = curr; i < words.size(); ++i) {
            if (any_of(word_counts[i].cbegin(), word_counts[i].cend(),
                       [&letter_count](const auto& x) {
                           return (*letter_count)[x.first] < x.second;
                       })) {
                continue;
            }
            for (const auto& [k, v] : word_counts[i]) {
                (*letter_count)[k] -= v;
            }
            backtracking(words, word_scores, word_counts,
                         i + 1, curr_score + word_scores[i], letter_count, result);
            for (const auto& [k, v] : word_counts[i]) {
                (*letter_count)[k] += v;
            }
        }
    }
};