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Add Binary
This is a string problem that rewards careful parsing and strong edge-case instincts. It's a great warm-up that builds rule-based parsing without a ton of moving parts. The trap is hidden edge cases—empty input, repeated characters, and boundary indexing.
Learn this pattern
String Problems
String problems rely on frequency counting, two-pointer palindrome checks, and knowing when a trie helps. The difference between brute-force O(n²) and a clean O(n) solution is usually one of these three techniques.
Meet your coaches
Talk through the problem while you code. Signed-in reps become prep memory for the next session.
Chat with Fin or Coco right now on mobile.
Start talking through the problem here. Switch to desktop when you're ready to code and run tests.
Start coaching sessionStart a coached rep now. Sign in before or after the session so StrongYes can save what you struggled with to your prep memory.
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String Problems gives you a useful next rep while you are still on your phone.