Why Trie Exists and What Hash Map Cannot Do for Strings in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a word into the Trie node children.

DSA Typescript

if (!node.children.has(word[i])) {
  node.children.set(word[i], new [1]());
}

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ATrieNode

BObject

CSet

DArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using Object/Set/Array instead of TrieNode for the child node.

Confusing with the Map structure used for children.

We create a new TrieNode() as the child node for the current character word[i].

2fill in blank

medium

Complete the code to check if a word exists in the Trie.

DSA Typescript

for (let i = 0; i < word.length; i++) {
  if (!node.children.has(word[i])) {
    return false;
  }
  node = node.children.get([1])!;
}
return node.isEndOfWord;

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Aword

Bword[i]

Ci

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i' instead of 'word[i]' which is an index, not a key.

Using 'node' which is the current node, not the child.

We get the child node corresponding to the current character word[i] to continue traversal.

3fill in blank

hard

Fix the error in the code to correctly count how many words start with a given prefix.

DSA Typescript

function countPrefix(node: TrieNode, prefix: string): number {
  for (let i = 0; i < prefix.length; i++) {
    if (!node.children.has(prefix[i])) {
      return 0;
    }
    node = node.children.get(prefix[i])!;
  }
  return [1];
}

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Anode.count

Bnode.isEndOfWord

Cnode.children.size

Dprefix.length

Attempts:

3 left

💡 Hint

Common Mistakes

Returning isEndOfWord which is a boolean, not a count.

Returning children.size which counts child nodes, not words.

We return node.count which tracks how many words share this prefix in the Trie.

4fill in blank

hard

Fill all three blanks to create a Trie node class with a children map, prefix count, and a boolean flag for word end.

DSA Typescript

class TrieNode {
  children: [1]<string, TrieNode>;
  count: [3];
  isEndOfWord: [2];

  constructor() {
    this.children = new Map();
    this.count = 0;
    this.isEndOfWord = false;
  }
}

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AMap

BSet

Cboolean

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using Set instead of Map for children.

Using boolean instead of number for count.

Using number instead of boolean for isEndOfWord.

The children are stored in a Map<string, TrieNode>, count is number for prefix frequency, and isEndOfWord is a boolean flag.

5fill in blank

hard

Fill all three blanks to implement a function that inserts a word into the Trie and updates counts.

DSA Typescript

function insertWord(root: TrieNode, word: string): void {
  let node = root;
  for (let i = 0; i < word.length; i++) {
    if (!node.children.has(word[i])) {
      node.children.set(word[i], new [1]());
    }
    node = node.children.get(word[i])!;
    node.[2] += 1;
  }
  node.[3] = true;
}

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ATrieNode

Bcount

CisEndOfWord

Dchildren

Attempts:

3 left

💡 Hint

Common Mistakes

Using children instead of count for counting prefixes.

Not marking isEndOfWord true at the end.

Wrong type for new node.

We create new TrieNode instances, increment the count property on each node, and mark isEndOfWord true at the end.