dsa1 min read
Subarray Sum Equals K [Medium] — Prefix Sum HashMap
Count subarrays with sum exactly k using prefix sums stored in a HashMap to find valid starting positions in O(n).
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Continuous Subarray Sum [Medium] — Prefix Modulo Map
Check if a continuous subarray of length >= 2 sums to a multiple of k using prefix sum modulo k with a HashMap.
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Longest Consecutive Sequence [Medium] — HashSet O(n)
Find the longest consecutive integer sequence in O(n) by using a HashSet and only starting sequences from their minimum element.
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Insert Delete GetRandom O(1) [Medium] — Array + HashMap Design
Design a set with O(1) insert, delete, and getRandom using a dynamic array combined with a HashMap for index tracking.
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Find All Anagrams in a String [Medium] — Fixed Window + Freq Match
Find all starting indices of anagram substrings by using a fixed window with character frequency comparison.
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