How do you solve Verifying an Alien Dictionary on LeetCode?

Verifying an Alien Dictionary (LeetCode #953) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding the mapping of characters to their indices is crucial for comparing words in the alien language.

What is the brute force solution for Verifying an Alien Dictionary?

The brute force approach for Verifying an Alien Dictionary is Brute Force, with O(n²) time complexity and O(1) space complexity. We can compare each word with the next one in the list to check if they are in the correct order according to the alien dictionary. This involves checking each character of the words until we find a difference or exhaust one of the words. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Verifying an Alien Dictionary?

Verifying an Alien Dictionary uses the following concepts: Array, Hash Table, String. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Verifying an Alien Dictionary?

Always clarify the problem statement and constraints before jumping into coding. Think about edge cases, such as empty strings or single-word inputs. Explain your thought process while coding, as it shows your understanding and can help you catch mistakes.

What are common mistakes when solving Verifying an Alien Dictionary?

Failing to handle cases where one word is a prefix of another (e.g., 'app' vs 'apple'). Not creating a proper mapping of characters to their indices, leading to incorrect comparisons.

#953

Verifying an Alien Dictionary

Easy

ArrayHash TableStringHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

Instead of comparing each word with the next in a brute-force manner, we can use a single pass with a mapping of characters to their indices to efficiently determine the order of words. This reduces unnecessary comparisons.

⚙️

Algorithm

3 steps

1Step 1: Create a mapping of each character in the alien order to its index.
2Step 2: Iterate through the list of words, comparing each word with the next one using the mapping.
3Step 3: If any word is found to be out of order, return false; otherwise, return true after all checks.

solution.py16 lines

1# Full working Python code
2order_map = {char: index for index, char in enumerate(order)}
3def isAlienSorted(words, order):
4    for i in range(len(words) - 1):
5        if not is_sorted(words[i], words[i + 1], order_map):
6            return False
7    return True
8
9def is_sorted(word1, word2, order_map):
10    min_length = min(len(word1), len(word2))
11    for i in range(min_length):
12        if order_map[word1[i]] < order_map[word2[i]]:
13            return True
14        elif order_map[word1[i]] > order_map[word2[i]]:
15            return False
16    return len(word1) <= len(word2)

ℹ

Complexity note: The time complexity is O(n) because we only pass through the list of words once, and the space complexity is O(n) due to the storage of the order mapping.

1Understanding the mapping of characters to their indices is crucial for comparing words in the alien language.
2Lexicographical order is determined by character comparison, similar to how we compare numbers.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.