Alexander Obregon's Substack
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LeetCode #43: Multiply Strings — Solved in Java
Naive String Multiplication and Digit Array Multiplication solutions.
3 hrs ago
•
Alexander Obregon
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API Contract Testing For Spring Boot With Consumer Driven Tests
Contract testing for Spring Boot APIs sits between unit checks and full end to end environments, with attention on the HTTP surface that clients call…
9 hrs ago
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Alexander Obregon
Arrays with Pointer Indexing in C
Arrays sit at the center of much low level work in C, and they raise real questions about how memory, pointers, and indexing behave.
Jan 22
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Alexander Obregon
SQL EXISTS, IN and JOIN Checks
Database queries rely on cross table checks in many everyday reports and features.
Jan 22
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Alexander Obregon
Fenwick Tree Mechanics in Java
Binary indexed trees, also called Fenwick trees, store partial sums in an array so prefix sums and point updates both run in logarithmic time.
Jan 21
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Alexander Obregon
LeetCode #177 Nth Highest Salary - Solved in PostgreSQL
Correlated COUNT(DISTINCT salary) Filter and DENSE_RANK Window Function
Jan 20
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Alexander Obregon
Function Call Mechanics in C
Function calls are at the center of almost every C codebase.
Jan 19
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Alexander Obregon
2
Weekly Recap – January 18th, 2026
Java, Go, LeetCode, SQL, C and Spring Boot
Jan 19
•
Alexander Obregon
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Alexander Obregon's Substack
Weekly recaps of what I’ve published, plus updates, extras, and some exclusive content you won’t find on my Medium.
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