Is Find Common Characters easy or hard?

Find Common Characters is classified as an Easy problem. The challenge mainly involves tracking minimum character frequencies across multiple strings using arrays or hash maps.

Find Common Characters Python/Java solution

In Python and Java, the common solution uses either a dictionary/map or an integer array of size 26. For each word, compute character frequencies and update the global minimum counts. Finally, rebuild the result list using the stored frequencies.

How to solve Find Common Characters in O(n)?

Treat each word as part of a single pass frequency comparison. Compute the character frequency for the first word, then update it with the minimum frequency from every other word. Since each character is processed once per string, the total complexity becomes O(n * k).

What is the best approach for Find Common Characters?

The frequency array approach is typically the best solution. Because the problem only uses lowercase English letters, you can maintain a 26-length array and keep the minimum frequency across all strings. This results in O(n * k) time and O(26) space while avoiding hash map overhead.

Is Find Common Characters asked at Google/Amazon/Meta?

Variants of character frequency and string intersection problems appear frequently in interviews at companies like Amazon, Google, and Meta. They test understanding of hash tables, counting techniques, and efficient string processing.

What data structure is used in Find Common Characters?

The main data structures are hash maps or fixed-size frequency arrays. A hash map stores character counts dynamically, while a 26-length array provides faster constant-time indexing for lowercase letters.

What is the time complexity of Find Common Characters?

The time complexity is O(n * k), where n is the number of words and k is the average length of each word. Each string is scanned once to count character frequencies, and only 26 characters are compared when updating the global minimum counts.

Description Solution Video 9:24

1002. Find Common Characters

Easy74.6% acceptance6 companies

Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order.

Example 1:

Input: words = ["bella","label","roller"]
Output: ["e","l","l"]

Example 2:

Input: words = ["cool","lock","cook"]
Output: ["c","o"]

Constraints:

1 <= words.length <= 100
1 <= words[i].length <= 100
words[i] consists of lowercase English letters.

Asked at 6 companies

Tripadvisor Amazon

Google Bloomberg Microsoft Meta

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9:24

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1002. Find Common Characters

Asked at 6 companies

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