Find the Difference
A easy-tier problem at 60% community acceptance, tagged with Hash Table, String, Bit Manipulation. Reported in interviews at Google and 0 others.
Find the Difference is the kind of easy problem that trips up candidates who overthink it. You're given two strings, one is a rearrangement of the other with a single extra character inserted, and you need to find what that character is. Google asks this, and it shows up in online assessments more often than the acceptance rate (59%) suggests, because the gap between a brute-force solution and an elegant one is where interviews live. The obvious approach works but kills your time budget. The trick is realizing you don't need to hash anything or sort anything. If you blank on the pattern during the live assessment, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Find the Difference"
Find the Difference is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe canonical trap is reaching for a hash table or sorting both strings, which works but wastes operations. The actual insight is mathematical: XOR every character in both strings. Since XOR is self-canceling (a XOR a equals 0), all matching characters vanish, leaving only the extra one. Alternatively, subtract ASCII values or use character counts, but XOR is the most elegant and what interviewers want to see. A lot of candidates jump to Bit Manipulation because it's in the topic list, see XOR, and nail it. Others waste time implementing a hash table when the problem scales small enough that bit manipulation dominates. The gap between 'this works' and 'this is smart' costs you feedback from the interviewer. When you hit this live and the obvious approach feels clunky, StealthCoder gives you the pattern you missed and lets you move forward.
Pattern tags
You know the problem.
Make sure you actually pass it.
Find the Difference recycles across companies for a reason. It's easy-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Find the Difference interview FAQ
Is this really an easy problem or does it just have high acceptance?+
Acceptance is 59%, which is lower than typical easy problems. It's easy once you know the XOR trick. Without it, you'll code something that works but takes too long or looks inefficient. The gap between submitting and impressing is the bit manipulation insight.
Does Google still ask Find the Difference in their assessments?+
Yes. It's in their reports. It's a screening problem, not a final-round grind, but screening problems set your tone. Nail the pattern and you move forward with momentum. Grind through a hash table and you burn time on something you should own.
What's the actual trick everyone talks about?+
XOR. Every character in string A XOR'd with every character in string B cancels matching pairs and leaves the extra character. It's O(n) time, O(1) space, and demonstrates you know bit manipulation. The second trick is ASCII value subtraction, which is equally valid but less interview-friendly.
Should I use Hash Table or Bit Manipulation?+
Bit Manipulation is the intended solution. Hash Table works but signals you didn't see the elegant path. Interviewers expect you to recognize this as a bit problem. If you go hash first, you're banking on clean code to recover. Bit manipulation does both.
How does this relate to the other topics listed?+
Sorting solves it (sort both, compare) but O(n log n). Bit Manipulation solves it in O(n) and O(1) space. Hash Table works in O(n) and O(26) space. The topics reflect valid approaches, but the interview wants you to pick the tightest one. That's Bit Manipulation here.
Want the actual problem statement? View "Find the Difference" on LeetCode →