Minimum Number of Flips to Make the Binary String Alternating
A medium-tier problem at 41% community acceptance, tagged with String, Dynamic Programming, Sliding Window. Reported in interviews at IBM and 0 others.
You're given a binary string and need to find the minimum flips to make it alternate between 0 and 1. IBM has asked this one. The problem looks deceptively simple at first: just count mismatches against two possible patterns and pick the smaller count. That brute-force read is fast to code but misses the optimal structure entirely. The real trick is recognizing that you only have two valid target patterns (starting with 0 or starting with 1), and a single pass solves it. If this hits your live assessment and you blank on the pattern trick, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Minimum Number of Flips to Make the Binary String Alternating"
Minimum Number of Flips to Make the Binary String Alternating 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 by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe algorithmic insight here is that instead of trying dynamic programming or complex state tracking, you just compare your input string against two fixed patterns: '010101...' and '101010...'. Count the flips needed for each, return the minimum. Most candidates waste time overthinking sliding-window or DP approaches when the problem is genuinely asking for a two-pattern comparison. The acceptance rate sits around 40%, which suggests many people either overcomplicate it or get tripped up by string indexing and counting logic. The actual code is clean and runs in linear time with constant space. If you hit this live and aren't immediately seeing the two-pattern approach, StealthCoder runs invisibly and hands you the solution before you spiral into a DP rabbit hole.
Pattern tags
You know the problem.
Make sure you actually pass it.
Minimum Number of Flips to Make the Binary String Alternating recycles across companies for a reason. It's medium-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 by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Number of Flips to Make the Binary String Alternating interview FAQ
Is this really a DP problem or a sliding window problem?+
Neither, primarily. The String tag is accurate. You only have two valid target patterns, so you compare the input against both in a single pass. DP and sliding window are red herrings that add complexity. Two passes (or one pass with dual counters) solves it optimally.
What's the trick that catches most people?+
Overthinking the state space. Candidates often try to track 'how many flips from position i to j with pattern X' when the answer is just 'count flips to pattern 010101 and count flips to pattern 101010, return the min'. Simplicity beats cleverness here.
Is this still being asked at big tech companies?+
IBM has reportedly asked it. The acceptance rate is around 40%, which indicates it's live but not top-tier frequent. It's the kind of problem that sneaks into assessments as a medium difficulty filter.
How does this relate to the Dynamic Programming topic tag?+
Loosely. The DP tag might reflect older solutions or alternative approaches, but the optimal path is not DP. The tag can mislead you into overengineering. Trust the pattern-matching approach instead.
What's the time complexity I should hit?+
Linear time, O(n), where n is the string length. Single or double pass, constant space. If you're writing anything worse than that, you've missed the two-pattern insight and need to step back.
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