Minimum Number of Swaps to Make the Binary String Alternating
A medium-tier problem at 43% community acceptance, tagged with String, Greedy. Reported in interviews at Societe Generale and 0 others.
You've got a binary string that's a mess, and you need to count the minimum swaps to make it alternate between 0 and 1. Societe Generale has asked this one. It's a medium-difficulty problem with a 43% acceptance rate, which means most candidates either solve it cleanly or tank it. The trap is overthinking the swaps themselves. The real work is figuring out how many positions violate the two possible alternating patterns, then recognizing that each swap fixes two violations at once. If you freeze on the pattern logic during your assessment, StealthCoder runs invisibly and surfaces the solution in seconds.
Companies that ask "Minimum Number of Swaps to Make the Binary String Alternating"
Minimum Number of Swaps 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 a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe greedy insight here is that there are only two valid alternating patterns: start with 0 or start with 1. You don't generate swaps randomly. Instead, you count how many positions deviate from each pattern, divide by 2 (because each swap fixes two mismatches), and return the minimum. The catch is that candidates often try to simulate swaps one-by-one, burning time and introducing off-by-one errors. The optimal approach is pure counting: scan the string once for pattern A, once for pattern B, do arithmetic, done. This problem tests whether you see the greedy structure or get trapped in simulation. String and Greedy are the core topics, and the acceptance rate reflects how many candidates miss the counting shortcut entirely. When this lands in your live OA and the swap approach feels murky, StealthCoder unblocks you with the pattern-counting solution.
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Minimum Number of Swaps 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 a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Number of Swaps to Make the Binary String Alternating interview FAQ
Why not just count swaps as you go?+
Simulating swaps is O(n^2) and error-prone. The greedy trick is recognizing only two valid patterns exist. Count mismatches for each, divide by 2, return the minimum. Swap simulation will time out or produce wrong answers under pressure.
Is this really asked at top companies?+
Societe Generale has confirmed it. It's not a household-name FAANG problem, but that doesn't make it easier. It's the kind of medium that screens for whether you think in patterns or get stuck in implementation details.
What's the actual trick to this problem?+
There are exactly two alternating patterns: 0101... and 1010... Compare your string to both, count position mismatches, divide each count by 2. The answer is the smaller result. No simulation required. Pure greedy math.
How does String relate to Greedy here?+
String is the surface: iterate and count characters. Greedy is the insight: assume one of two fixed patterns and pick the one requiring fewest fixes. You're not choosing which swaps to make; you're choosing which pattern minimizes cost.
What percentage of people get this wrong?+
Acceptance rate is 43%, so most fail. Common mistakes: simulating swaps, miscounting mismatches, forgetting to divide by 2, or trying to build swaps dynamically. The clean solution takes 3-4 minutes once you see the pattern.
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