LeetCode/cs/maximum-score-words-formed-by-letters.cs

public class Solution {
    private int[] freqs;
    private void SetFreqs(char[] letters) {
        freqs = new int[26];
        foreach (char c in letters) {
            ++freqs[c - 'a'];
        }
    }

    private int maxScore;
    private int currentScore;

    private string[] words;
    private int[] score;
    private void check(int i) {
        if (i >= words.Length) {
            maxScore = Math.Max(maxScore, currentScore);
            return;
        }

        // Skipping the current word
        check(i + 1);

        // Try to add word
        int j;
        for (j = 0; j < words[i].Length; ++j) {
            var c = words[i][j] - 'a';
            --freqs[c];
            currentScore += score[c];

            if (freqs[c] < 0) {
                break;
            }
        }

        // Means we were able to use all letters from the word
        if (j == words[i].Length) {
            check(i + 1);
        }

        // Revert the changes
        for (j = Math.Min(j, words[i].Length - 1); j >= 0; --j) {
            var c = words[i][j] - 'a';
            ++freqs[c];
            currentScore -= score[c];
        }
    }

    public int MaxScoreWords(string[] words, char[] letters, int[] score) {
        SetFreqs(letters);

        maxScore = 0;
        currentScore = 0;

        this.words = words;
        this.score = score;

        check(0);
        return maxScore;
    }
}