Pattern · String

String interview questions

468 string problems tagged across recent interview reports. Drilled most heavily by amazon, meta, and google.

Founder's read

String problems make up 468 tagged problems across major tech interviews. Amazon and Meta each drill 138 String variants in their OA pipelines. Google, Bloomberg, and TikTok follow close behind with 115, 114, and 110 respectively. String manipulation isn't a single trick, it's a category spanning substring search, character encoding, parsing, transformation, and state tracking. Most candidates underestimate the breadth until a live OA throws an unfamiliar variant at them. That's where StealthCoder steps in: when a String problem lands during your assessment and you hit a wall, it solves it invisibly in seconds.

Most-asked string problems

Sorted by # companies asking

#	Problem	Diff	# Companies	Pass %
01	Basic Calculator II	MEDIUM	27	46%
02	Basic Calculator	HARD	17	46%
03	Count and Say	MEDIUM	14	61%
04	Alien Dictionary	HARD	13	37%
05	Backspace String Compare	EASY	12	49%
06	Add Binary	EASY	11	56%
07	Add Strings	EASY	10	52%
08	Basic Calculator III	HARD	10	52%
09	Accounts Merge	MEDIUM	8	60%
10	Compare Version Numbers	MEDIUM	6	42%
11	Break a Palindrome	MEDIUM	5	52%
12	Count Binary Substrings	EASY	5	66%
13	Binary Tree Paths	EASY	3	67%
14	Brace Expansion	MEDIUM	3	67%
15	Bulls and Cows	MEDIUM	3	51%
16	Check Whether Two Strings are Almost Equivalent	EASY	3	64%
17	Add Bold Tag in String	MEDIUM	2	51%
18	Alert Using Same Key-Card Three or More Times in a One Hour Period	MEDIUM	2	46%
19	Basic Calculator IV	HARD	2	49%
20	Buddy Strings	EASY	2	34%
21	Check If a Word Occurs As a Prefix of Any Word in a Sentence	EASY	2	69%
22	Check if Number Has Equal Digit Count and Digit Value	EASY	2	72%
23	Check if the Sentence Is Pangram	EASY	2	84%
24	Concatenated Words	HARD	2	49%
25	Construct Smallest Number From DI String	MEDIUM	2	86%
26	Construct String With Repeat Limit	MEDIUM	2	71%
27	Additive Number	MEDIUM	1	33%
28	Apply Bitwise Operations to Make Strings Equal	MEDIUM	1	42%
29	Apply Operations to Make Two Strings Equal	MEDIUM	1	27%
30	Apply Substitutions	MEDIUM	1	79%
31	Better Compression of String	MEDIUM	1	76%
32	Build Binary Expression Tree From Infix Expression	HARD	1	62%
33	Calculate Score After Performing Instructions	MEDIUM	1	56%
34	Camelcase Matching	MEDIUM	1	64%
35	Can Convert String in K Moves	MEDIUM	1	36%
36	Can Make Palindrome from Substring	MEDIUM	1	40%
37	Check if a Parentheses String Can Be Valid	MEDIUM	1	45%
38	Check if All Characters Have Equal Number of Occurrences	EASY	1	79%
39	Check if an Original String Exists Given Two Encoded Strings	HARD	1	43%
40	Check if Binary String Has at Most One Segment of Ones	EASY	1	39%
41	Check if One String Swap Can Make Strings Equal	EASY	1	49%
42	Check if Strings Can be Made Equal With Operations I	EASY	1	47%
43	Check if Strings Can be Made Equal With Operations II	MEDIUM	1	55%
44	Check If Word Is Valid After Substitutions	MEDIUM	1	60%
45	Clear Digits	EASY	1	83%
46	Consecutive Characters	EASY	1	60%
47	Construct String with Minimum Cost	HARD	1	19%
48	Count Anagrams	HARD	1	35%
49	Count Collisions on a Road	MEDIUM	1	44%
50	Count Common Words With One Occurrence	EASY	1	72%

Showing top 50 of 468 string problems by # companies asking.

The hedge for the live OA

You can't drill every string variant before the assessment. StealthCoder runs invisibly during screen share and solves whichever variant they throw at you. No browser extension. No detection signature. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.

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What this means

String problems split into recognizable families: character-by-character transforms (add-bold-tag-in-string, backspace-string-compare), numeric string ops (add-strings, add-binary), substring matching (alien-dictionary), and stateful scanning (alert-using-same-key-card-three-or-more-times-in-a-one-hour-period). The trap is assuming one approach generalizes. A two-pointer solution for one problem fails on another that needs a stack or hash map. Drill order matters: start with single-pass transforms, then two-pointer edge cases, then state machines. Bloomberg and Goldman Sachs weight these heavily in their OA gatekeeping rounds. StealthCoder is your insurance policy for the String variant you didn't anticipate, it reads the problem on screen and delivers working code before you second-guess your approach.

⏵ The honest play

468 string problems.
You won't drill them all. Pass anyway.

String is one of the patterns interviews actually filter on. Memorizing every variant in a week is a fantasy. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds, no matter which string flavor lands in your live OA. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.

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String interview FAQ

How many String problems should I drill before my OA?+

With 468 problems tagged String, sampling is mandatory. Focus on 20-30 problems across the five main families: transforms, numeric ops, substring logic, pattern matching, and state machines. Amazon and Meta combined ask 276 String problems, their patterns are the baseline. Drill until you recognize the family in the problem statement within 30 seconds.

How do I recognize a String problem during my OA?+

You're building, comparing, or extracting from text. Look for character indices, substring bounds, encoding rules, or event timing within strings. If the solution involves pointer movement, stack reversal, or hash lookups on characters, it's String. Problems like add-strings and backspace-string-compare are classic tells.

Which companies weight String problems the most?+

Amazon and Meta each have 138 tagged String problems in their interview pools. Google follows with 115, Bloomberg with 114. TikTok (110), Microsoft (108), and Zoho (106) are also heavy. If you're targeting any of these, String depth is non-negotiable.

What's the most common String pitfall in live OAs?+

Choosing the wrong data structure. Two-pointer works for some; stacks for others; hash maps for character frequency. Many candidates default to one approach and waste 15 minutes on a wrong path. Recognizing the subtype first, transform vs. numeric vs. search, saves you on a timed assessment.

Should I memorize String algorithms or focus on pattern recognition?+

Pattern recognition wins. Memorizing every String trick is impossible with 468 problems. Learn to spot substring problems, numeric string ops, and state machines. Understand two-pointer and stack mechanics deeply. In a live OA, when a String variant you've never seen appears, pattern spotting beats memorization every time.

String interview questions

Most-asked string problems

Companies that hire most on string

468 string problems. You won't drill them all. Pass anyway.

String interview FAQ

468 string problems.
You won't drill them all. Pass anyway.