dsa2 min read
Intersection of Two Arrays II — HashMap Frequency Count [Amazon Easy]
Find the intersection of two integer arrays including duplicates. Each element appears as many times as it shows in both arrays.
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dsa5 min read
Arrays & Strings Complete — 100-Problem Master Cheatsheet
Master cheatsheet of all 100 Arrays & Strings problems: patterns, time/space complexity, and MAANG company tags in one place.
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dsa2 min read
Pascal's Triangle — Row-by-Row DP Generation [Easy]
Generate numRows rows of Pascal's triangle. Each interior element is the sum of the two elements above it.
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Valid Anagram — Frequency Array vs HashMap [Amazon, Google Easy]
Check if two strings are anagrams — same characters with same frequencies. Two O(n) approaches: 26-int array for lowercase, HashMap for Unicode.
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Reverse String — Two Pointer In-Place O(n) [Meta, Microsoft Easy]
Reverse a character array in-place using two pointers. O(n) time, O(1) space. The fundamental two-pointer swap pattern.
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