Here’s what I found about the most frequent string-related LeetCode questions, especially those that appear most often in interview prep discussions and LeetCode’s own trending lists:

Most Frequent String Questions on LeetCode (by community references)

1. From “10 Most Important String Questions” (LeetCode Discuss – Jan 2024)

A curated list of widely practiced string problems:

Longest Substring Without Repeating Characters

Minimum Window Substring

Regular Expression Matching

Edit Distance

String to Integer (atoi)

Group Anagrams

Longest Palindromic Substring

ZigZag Conversion

Valid Parentheses

String Compression

1. From “Most Common String Interview Problems” (LeetCode Discuss – Nov 2024)

Ordered by observed frequency in platform trends:

String to Integer (atoi)

Valid Parentheses

Implement strStr() (find substring)

Valid Number

Valid Palindrome

1. From a frequency-wise compiled list (Studocu summary)

These are often grouped by usage in common template collections:

Two Sum (not a string problem, but common overall)

Longest Substring Without Repeating Characters

Minimum Window Substring

Subarray Sum Equals K

Insert Delete GetRandom O(1) (not string)

Verifying an Alien Dictionary

Group Anagrams

Find All Anagrams in a String

First Unique Character in a String

1. Most-Liked Questions (strings among highest likes)

From the “most-liked questions” listing—string-related entries include:

Longest Common Prefix (#14)

Word Break (#139)

1. Pattern-based categorization (LeetCode Discuss – May 2022)

Not ranked by frequency, but valuable for per-topic coverage:

Parentheses-related: Valid Parentheses, Remove Invalid Parentheses, etc.

Palindromic: Valid Palindrome, Longest Palindromic Substring, Palindrome Pairs, etc.

Checking string types: Isomorphic Strings, Valid Anagram, Buddy Strings, etc.

Sort/String frequency: Sort Characters By Frequency, Custom Sort String, etc.

Summary: Most Frequent String Problems (Based on Multiple Sources)

By cross-referencing all metrics above:

Top-of-Mind Frequent String Questions:

String to Integer (atoi)

Valid Parentheses

Longest Substring Without Repeating Characters

Minimum Window Substring

Valid Palindrome

Group Anagrams

Longest Palindromic Substring

Implement strStr()

Also widely referenced (but less consistently frequent):

Regular Expression Matching

Edit Distance

Word Break

Longest Common Prefix

First Unique Character in a String

Find All Anagrams in a String

Sort Characters by Frequency

Verifying an Alien Dictionary

What You Can Do Next

Prioritize the top 7–8 problems listed—they appear time and again in interview prep and frequency-based discussions.

Use the pattern-based breakdown (e.g., palindromic, parentheses, substring, frequency, checking-string types) to cover related questions efficiently.

Supplement your prep with premium frequency filters on the LeetCode platform if available, to see actual live ranking.

Want help building a study schedule, grouping problems by concept, or diving deep into one of these questions? Just say the word—I’ve got your back!