solves word break with trie

Author: anishLearnsToCode

src/WordBreak.java

@@ -0,0 +1,58 @@
+import java.util.List;
+
+public class WordBreak {
+    private static final class Trie {
+        private static final int LETTERS_IN_ENGLISH_ALPHABET = 26;
+
+        Trie[] letters = new Trie[LETTERS_IN_ENGLISH_ALPHABET];
+        boolean isWord = false;
+
+        public void insert(String word) {
+            insert(word, 0, this);
+        }
+
+        private void insert(String s, int index, Trie root) {
+            if (index >= s.length()) {
+                root.isWord = true;
+                return;
+            }
+            if (root.letters[s.charAt(index) - 'a'] == null) {
+                root.letters[s.charAt(index) - 'a'] = new Trie();
+            }
+            insert(s, index + 1, root.letters[s.charAt(index) - 'a']);
+        }
+
+        public boolean exists(String word) {
+            return exists(word, 0, this);
+        }
+
+        private boolean exists(String s, int index, Trie root) {
+            if (index >= s.length()) {
+                return root.isWord;
+            }
+            if (root.letters[s.charAt(index) - 'a'] == null) return false;
+            return exists(s, index + 1, root.letters[s.charAt(index) - 'a']);
+        }
+    }
+
+
+    public boolean wordBreak(String s, List<String> wordDict) {
+        final Trie trie = new Trie();
+        for (String string : wordDict) {
+            trie.insert(string);
+        }
+        return wordBreak(s, trie);
+    }
+
+    private boolean wordBreak(String s, Trie root) {
+        if (s.isEmpty()) return true;
+
+        for (int i = 0 ; i < s.length() ; i++) {
+            if (root.exists(s.substring(0, i + 1)) && wordBreak(s.substring(i + 1), root)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}