Improve Trie test coverage back to 100%.

Author: trekhleb

src/data-structures/trie/Trie.js

@@ -29,27 +29,37 @@ export default class Trie {
    * @return {Trie}
    */
   deleteWord(word) {
-    function depthFirstDelete(currentNode, charIndex) {
-      if (charIndex >= word.length) return;
+    const depthFirstDelete = (currentNode, charIndex = 0) => {
+      if (charIndex >= word.length) {
+        // Return if we're trying to delete the character that is out of word's scope.
+        return;
+      }
 
       const character = word[charIndex];
       const nextNode = currentNode.getChild(character);
 
-      if (nextNode == null) return;
+      if (nextNode == null) {
+        // Return if we're trying to delete a word that has not been added to the Trie.
+        return;
+      }
 
+      // Go deeper.
       depthFirstDelete(nextNode, charIndex + 1);
 
-      if (charIndex === word.length - 1) {
+      // Since we're going to delete a word let's un-mark its last character isCompleteWord flag.
+      if (charIndex === (word.length - 1)) {
         nextNode.isCompleteWord = false;
       }
 
       // childNode is deleted only if:
       // - childNode has NO children
       // - childNode.isCompleteWord === false
       currentNode.removeChild(character);
-    }
+    };
+
+    // Start depth-first deletion from the head node.
+    depthFirstDelete(this.head);
 
-    depthFirstDelete(this.head, 0);
     return this;
   }
 

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

@@ -35,6 +35,13 @@ describe('Trie', () => {
     expect(trie.doesWordExist('cart')).toBe(true);
     expect(trie.doesWordExist('cat')).toBe(true);
 
+    // Try to delete not-existing word first.
+    trie.deleteWord('carpool');
+    expect(trie.doesWordExist('carpet')).toBe(true);
+    expect(trie.doesWordExist('car')).toBe(true);
+    expect(trie.doesWordExist('cart')).toBe(true);
+    expect(trie.doesWordExist('cat')).toBe(true);
+
     trie.deleteWord('carpet');
     expect(trie.doesWordExist('carpet')).toEqual(false);
     expect(trie.doesWordExist('car')).toEqual(true);