Problem database last updated: June 20, 2025
10 problems · 6 Easy, 4 Medium, 0 Hard · Ranked #142 of 458
6 Easy
60% · avg 23%
4 Medium
40% · avg 59%
0 Hard
0% · avg 18%
Based on 10 reported problems, persistent systems interviews are easier than average - only 0% Hard compared to 18% across all companies.
Compared to the industry average, persistent systems puts unusual emphasis on sorting (30% of problems, 2.1x the industry average), string (50% of problems, 1.8x the industry average), two-pointers (20% of problems, 1.5x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are string (50%), array (40%), hash-table (30%), sorting (30%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Minimum Bit Flips to Convert Number A bit flip of a number x is choosing a bit in the binary representation of x and flipping it from either 0 to 1 or 1 to 0. | Easy | Very Likely | bit-manipulation | Solve |
Group Anagrams Given an array of strings strs, group the anagrams together. You can return the answer in any order. | Medium | Very Likely | arrayhash-tablestring | Solve |
Palindrome Number Given an integer x, return true if x is a palindrome, and false otherwise. | Easy | Likely | math | Solve |
Valid Parentheses Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. | Easy | Likely | stringstack | Solve |
Two Sum Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target. | Easy | Likely | arrayhash-map | Solve |
Valid Anagram Given two strings s and t, return true if t is an anagram of s, and false otherwise. | Easy | Likely | hash-tablestringsorting | Solve |
Merge Sorted Array You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num... | Easy | Likely | arraytwo-pointerssorting | Solve |
Longest Substring Without Repeating Characters Given a string s, find the length of the longest substring without duplicate characters. | Medium | Likely | hash-tablestringsliding-window | Solve |
Maximum Subarray Given an integer array nums, find the subarray with the largest sum, and return its sum. | Medium | Likely | arraydivide-and-conquerdynamic-programming | Solve |
Longest Palindromic Substring Given a string s, return the longest palindromic substring in s. | Medium | Likely | two-pointersstringdynamic-programming | Solve |
Minimum Bit Flips to Convert Number
SolveA bit flip of a number x is choosing a bit in the binary representation of x and flipping it from either 0 to 1 or 1 to 0.
Group Anagrams
SolveGiven an array of strings strs, group the anagrams together. You can return the answer in any order.
Palindrome Number
SolveGiven an integer x, return true if x is a palindrome, and false otherwise.
Valid Parentheses
SolveGiven a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
Two Sum
SolveGiven an array of integers nums and an integer target, return the indices of the two numbers that add up to target.
Valid Anagram
SolveGiven two strings s and t, return true if t is an anagram of s, and false otherwise.
Merge Sorted Array
SolveYou are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num...
Longest Substring Without Repeating Characters
SolveGiven a string s, find the length of the longest substring without duplicate characters.
Maximum Subarray
SolveGiven an integer array nums, find the subarray with the largest sum, and return its sum.
Longest Palindromic Substring
SolveGiven a string s, return the longest palindromic substring in s.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent persistent systems interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
persistent systems interviews focus heavily on string, array, hash-table problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. persistent systems interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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persistent systems has been reported to ask 10 distinct coding problems. The most common topics are string, array, hash-table. 6 are Easy difficulty, 4 are Medium, and 0 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 10 reported problems, persistent systems interviews are easier than average - only 0% Hard compared to 18% across all companies. 40% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: string, array, hash-table. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
Simulate a real persistent systems coding interview with an AI interviewer. Get a scorecard with specific feedback on your problem-solving, code quality, and communication.
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