solves word break in java

Author: anishLearnsToCode

README.md

@@ -124,7 +124,7 @@
 | 136  | [Single Number](https://leetcode.com/problems/single-number)                                                                                              |                                      [![Java](assets/java.png)](src/SingleNumber.java) [![Python](assets/python.png)](python/single_number.py)                                       |                                                                                                                                   |
 | 137  | [Single Number II](https://leetcode.com/problems/single-number-ii)                                                                                        |                                                                 [![Java](assets/java.png)](src/SingleNumberII.java)                                                                  |                                                                                                                                   |
 | 138  | [Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer)                                                              |                                                            [![Java](assets/java.png)](src/CopyListWithRandomPointer.java)                                                            |                                                                                                                                   |
-| 139  | [Word Break](https://leetcode.com/problems/word-break)                                                                                                    |                                                                                                                                                                                      |                                                                                                                                   |
+| 139  | [Word Break](https://leetcode.com/problems/word-break)                                                                                                    |                                                                    [![Java](assets/java.png)](src/WordBreak.java)                                                                    |                                                                                                                                   |
 | 141  | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle)                                                                                      |                                   [![Java](assets/java.png)](src/LinkedListCycle.java) [![Python](assets/python.png)](python/linked_list_cycle.py)                                   |                                                                                                                                   |
 | 142  | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii)                                                                                |                                                                                                                                                                                      |                                                                                                                                   |
 | 143  | [Reorder List](https://leetcode.com/problems/reorder-list)                                                                                                |                                                                                                                                                                                      |                                                                                                                                   |

src/WordBreak.java

@@ -1,58 +1,26 @@
+// https://leetcode.com/problems/word-break
+// T: O(s^3 + w)
+// S: O(s + w)
+
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 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;
+        final Set<String> words = new HashSet<>(wordDict);
+        final boolean[] dp = new boolean[s.length() + 1];
+        dp[0] = true;
+
+        for (int i = 1 ; i <= s.length() ; i++) {
+            for (int j = 0 ; j < i ; j++) {
+                if (dp[j] && words.contains(s.substring(j, i))) {
+                    dp[i] = true;
+                    break;
+                }
             }
         }
 
-        return false;
+        return dp[dp.length - 1];
     }
 }