Check if Binary String Has at Most One Segment of Ones
A easy-tier problem at 39% community acceptance, tagged with String. Reported in interviews at Cisco and 0 others.
You're staring at a binary string problem that sounds deceptively simple: check if it has at most one contiguous block of ones. Cisco asks this one, and the 39% acceptance rate should tell you something. Most candidates over-engineer it or misread what "at most one segment" actually means. The trick isn't complex, but the wording trips people up fast. If you hit this live and blank on the exact logic, StealthCoder reads the problem and surfaces the solution in seconds, invisible to the proctor.
Companies that ask "Check if Binary String Has at Most One Segment of Ones"
Check if Binary String Has at Most One Segment of Ones 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 because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderThe pattern here is straightforward once you see it: a valid string either has zero ones, one block of ones, or one block surrounded by zeros. The gotcha is that candidates often try to count segments or build state machines when they could just check if the string matches a regex or scan for transitions. The real pitfall: confusing "at most one segment" with "at most one one". You need to detect if ones appear in more than one disconnected group. A single pass checking transitions from zero to one (or vice versa) tells you if segments exist. If you encounter more than one zero-to-one transition, you've got multiple segments. StealthCoder is the safety net if the wording confuses you during screen share and you can't lock onto the right approach.
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Check if Binary String Has at Most One Segment of Ones 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 because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Check if Binary String Has at Most One Segment of Ones interview FAQ
Is this problem actually easy or is the low acceptance rate misleading?+
It's genuinely easy algorithmically, but the wording trips candidates. The 39% rate reflects misreading the problem statement rather than hard logic. Most who understand what "one segment" means solve it in under 5 minutes.
What's the most common wrong approach?+
Trying to count or track individual ones instead of counting transitions. Or splitting the string and checking segment count, which works but is overkill. The one-pass transition method is cleaner and catches the real constraint immediately.
Does Cisco ask this a lot in real interviews?+
Only one major company reports asking it. It's not a repeat-heavy problem, but it's exactly the kind of deceptively simple string problem that shows up as a warm-up or early-round screening question.
What string edge cases break this?+
Empty string, all zeros, all ones, and strings like '110011' (ones on both ends with zeros in middle). The last one is the killer because it looks valid but has two segments of ones.
How does this relate to general string scanning patterns?+
It's a transition-counting pattern. Once you see it here, you'll spot the same logic in problems about grouping consecutive characters, detecting alternating patterns, or finding isolated elements in a sequence.
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