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#leetcode · All writing
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01
Two Sum: from O(n²) brute force to a single hash-map pass
Two Sum is the first problem most people solve, and it's quietly a sales pitch for the hash map. Here's the brute force, the one trick that kills the nested loop, and the one-pass version I'd actually write.Jun 13, 2026 · 5 min read · #00001
02
Climbing Stairs: from exponential recursion to O(1) space
LeetCode 70 is Fibonacci in disguise. Here are the four solutions I actually reach for, why the naive one deserves to time out, and how to recognise the same shape in harder DP problems.Jun 13, 2026 · 6 min read · #00002
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