dsa1 min read
Rotate String [Easy] — String Contains Trick
Check if string B is a rotation of A by checking if B appears in A+A using a substring search.
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dsa1 min read
Repeated String Match [Medium] — Minimum Repetitions
Find the minimum times A must repeat so that B is a substring, using a tight bound on the number of repeats needed.
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dsa2 min read
Trapping Rain Water [Hard] — Two Pointers O(n)
Calculate trapped rain water using inward two pointers that track left-max and right-max, replacing the classic O(n) space approach.
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Sliding Window Maximum [Hard] — Monotonic Deque
Find the maximum in every sliding window of size k in O(n) using a monotonic decreasing deque.
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First Missing Positive [Hard] — Cyclic Sort / Index Marking
Find the smallest missing positive integer in O(n) time O(1) space using in-place cyclic sort to place each number at its correct index.
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