String-matching

2 articles

dsa5 min read

Rotate String — The Concatenation Trick [LC 796]

LeetCode 796 — asked at Amazon and Google. Check if string s can become string goal by rotating. The elegant O(n) trick: concatenate s with itself and check if goal is a substring. One line of code once you see the insight.

March 19, 2026Read →

dsa5 min read

Repeated String Match — Ceiling Division String Matching [LC 686]

LeetCode 686 — asked at Google and Amazon. Find the minimum number of times to repeat string a so that b is a substring. The ceiling trick: repeat a at least ceil(len(b)/len(a)) times, then check that and one more. O(n*m) time, O(n+m) space.

March 19, 2026Read →