Practice · 2 of 3

Border Patrol

CHALLENGE

Difficulty: advanced+25 XP

**Problem.** Given a string s, count its border lengths: every 1 <= l < |s| with s[0..l) == s[|s|-l..|s|). **Constraints:** 2 <= |s| <= 2000001. Checking every length by direct comparison is the classic near-miss.

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Back to lesson: Practice: Mixed Drill — Trees and Strings