Fix method Trie::doesWordExist() (trekhleb#175)

Method Trie::doesWordExist() return `true` when word is complete otherwise `false`

Author: Oleg

src/data-structures/trie/Trie.js

@@ -43,7 +43,9 @@ export default class Trie {
    * @return {boolean}
    */
   doesWordExist(word) {
-    return !!this.getLastCharacterNode(word);
+    const lastCharacter = this.getLastCharacterNode(word);
+
+    return !!lastCharacter && lastCharacter.isCompleteWord;
   }
 
   /**

src/data-structures/trie/__test__/Trie.test.js

@@ -45,7 +45,8 @@ describe('Trie', () => {
     trie.addWord('caption');
 
     expect(trie.doesWordExist('cat')).toBe(true);
-    expect(trie.doesWordExist('cap')).toBe(true);
+    expect(trie.doesWordExist('cats')).toBe(true);
+    expect(trie.doesWordExist('cap')).toBe(false);
     expect(trie.doesWordExist('call')).toBe(false);
   });
 });