solves number of valid words in a sentence

Author: anishLearnsToCode

README.md

@@ -487,7 +487,7 @@
 | 2032 | [Two Out of Three](https://leetcode.com/problems/two-out-of-three)                                                                                        |                                                                  [![Java](assets/java.png)](src/TwoOutOfThree.java)                                                                  |                                                                                                                                   |
 | 2037 | [Minimum Number of Moves to Seat Everyone](https://leetcode.com/problems/minimum-number-of-moves-to-seat-everyone)                                        |                                                       [![Java](assets/java.png)](src/MinimumNumberOfMovesToSeatEveryone.java)                                                        |                                                                                                                                   |
 | 2042 | [Check if Numbers Are Ascending in a Sentence](https://leetcode.com/problems/check-if-numbers-are-ascending-in-a-sentence)                                |                                                      [![Java](assets/java.png)](src/CheckIfNumbersAreAscendingInASentence.java)                                                      |                                                                                                                                   |
-| 2047 | [Number of Valid Words in a Sentence](https://leetcode.com/problems/number-of-valid-words-in-a-sentence)                                                  |                                                                                                                                                                                      |                                                                                                                                   |
+| 2047 | [Number of Valid Words in a Sentence](https://leetcode.com/problems/number-of-valid-words-in-a-sentence)                                                  |                                                          [![Java](assets/java.png)](src/NumberOfValidWordsInASentence.java)                                                          |                                                                                                                                   |
 | 2053 | [Kth Distinct String in an Array](https://leetcode.com/problems/kth-distinct-string-in-an-array)                                                          |                                                                                                                                                                                      |                                                                                                                                   |
 | 2057 | [Smallest Index With Equal Value](https://leetcode.com/problems/smallest-index-with-equal-value)                                                          |                                                                                                                                                                                      |                                                                                                                                   |
 | 2062 | [Count Vowel Substrings of a String](https://leetcode.com/problems/count-vowel-substrings-of-a-string)                                                    |                                                                                                                                                                                      |                                                                                                                                   |

src/NumberOfValidWordsInASentence.java

@@ -0,0 +1,50 @@
+// https://leetcode.com/problems/number-of-valid-words-in-a-sentence
+// T: O(|sentence|)
+// S: O(|sentence|)
+
+import java.util.Set;
+
+public class NumberOfValidWordsInASentence {
+    private static final Set<Character> PUNCTUATIONS = Set.of('!', '.', ',');
+
+    public int countValidWords(String sentence) {
+        StringBuilder word = new StringBuilder();
+        int validWords= 0;
+        for (int i = 0 ; i < sentence.length() ; i++) {
+            if (sentence.charAt(i) == ' ') {
+                validWords += isValidWord(word) ? 1 : 0;
+                word = new StringBuilder();
+            } else word.append(sentence.charAt(i));
+        }
+        return validWords + (isValidWord(word) ? 1 : 0);
+    }
+
+    private boolean isValidWord(StringBuilder s) {
+        if (s.length() == 0) return false;
+        for (int i = 0, hyphens = 0 ; i < s.length() ; i++) {
+            if (isDigit(s.charAt(i))) return false;
+            else if (isHyphen(s.charAt(i))) {
+                if (hyphens > 0) return false;
+                hyphens++;
+                if (i == 0 || i == s.length() - 1 || !isAlphabet(s.charAt(i + 1))) return false;
+            } else if (isPunctuationMark(s.charAt(i)) && i < s.length() - 1) return false;
+        }
+        return true;
+    }
+
+    private boolean isDigit(char c) {
+        return Character.isDigit(c);
+    }
+
+    private boolean isHyphen(char c) {
+        return c == '-';
+    }
+
+    private boolean isAlphabet(char c) {
+        return Character.isAlphabetic(c);
+    }
+
+    private boolean isPunctuationMark(char c) {
+        return PUNCTUATIONS.contains(c);
+    }
+}