A live coding walkthrough of Advent of Code 2025 Day 1 using Rust. The author sets up a Cargo workspace with a daily template, uses cargo-generate for scaffolding, and walks through solving both parts of the puzzle. Part 1 involves tracking how many times a rotating dial lands on zero; Part 2 counts zero crossings during rotations. The solution uses the nom parser combinator library to parse input into a typed Direction enum, rem_euclid for modular arithmetic, and rs_test for parameterized testing. The author also refactors the loop into a fold and discusses iterator tools like tuple_windows and cartesian_product.
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