cs: add «1255. Maximum Score Words Formed by Letters»

Signed-off-by: Matej Focko <me@mfocko.xyz>

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

@@ -0,0 +1,61 @@
+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;
+    }
+}