Minimum Changes To Make Alternating Binary String
A easy-tier problem at 64% community acceptance, tagged with String. Reported in interviews at Tesla and 0 others.
You've got a binary string, and you need to make it alternating with the minimum number of changes. Tesla asks this one, and it lands as an easy, but the pattern matters. The acceptance rate sits around 64%, which means a meaningful chunk of candidates miss the trick or overcomplicate it. If you haven't drilled string iteration and pattern matching, this is the kind of problem that can trip you up in a timed assessment. StealthCoder solves it in seconds if you blank on the approach during your live OA.
Companies that ask "Minimum Changes To Make Alternating Binary String"
Minimum Changes To Make Alternating Binary String 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick is recognizing there are only two possible alternating patterns: starting with 0 or starting with 1. You iterate through the string once, count mismatches for each pattern, then return the minimum. Most candidates overthink it or try to greedily modify the string in place. The gotcha is that you need to check both patterns and compare, not assume one is obviously better. A single pass through the string gives you both counts. Common miss: candidates write nested loops or try to validate after each change instead of just tallying. If you hit this during an assessment and freeze on the strategy, StealthCoder surfaces the two-pattern approach immediately.
Pattern tags
You know the problem.
Make sure you actually pass it.
Minimum Changes To Make Alternating Binary String 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Changes To Make Alternating Binary String interview FAQ
Is this problem actually easy or is the acceptance rate misleading?+
64% acceptance is solid for easy, so the rating is fair. Most misses come from overthinking the pattern matching or trying to build the alternating string dynamically instead of just counting. The algorithm is straightforward once you see it.
Do I need to actually build the alternating string or just count changes?+
Just count. Iterate through the original string, track how many positions differ from pattern A (01010...) and pattern B (10101...). Return the minimum count. No reconstruction needed.
How do I avoid the mistake of only checking one pattern?+
Both patterns are equally valid. Code both loops or both comparisons. Pattern starting with 0 and pattern starting with 1 might have different costs. Always compare both, return the minimum.
Is this still asked by Tesla or just archived?+
Tesla is the only company listed as asking this, so it does appear in their pipeline. Easy problems like this are often used as screening filters or warm-up rounds.
What's the time and space complexity?+
O(n) time for a single pass through the string, O(1) space if you just track two counters. Very efficient. The problem is not about optimization, it's about correctness and seeing the two-pattern insight.
Want the actual problem statement? View "Minimum Changes To Make Alternating Binary String" on LeetCode →