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Simplify

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This commit is contained in:
Jeremy Kaplan 2022-12-23 17:22:02 -08:00
commit a66e590b35
1 changed files with 5 additions and 9 deletions
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14
2022/src/bin/day20.rs
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@ -80,7 +80,7 @@ impl Decrypter {
// i | [x, y, z, a, b, c] // i | [x, y, z, a, b, c]
assert_eq!(i, m); assert_eq!(i, m);
let n = delta(n, self.ilen); let n = imod(n, self.ptr.len());
self.ptr.rotate_left(n); self.ptr.rotate_left(n);
self.ptr.push_front(m); self.ptr.push_front(m);
} else { } else {
@ -92,18 +92,14 @@ impl Decrypter {
// [x, y, z, a, b, c] | i // [x, y, z, a, b, c] | i
assert_eq!(i, m); assert_eq!(i, m);
let n = delta(n, self.ilen); let n = imod(n, self.ptr.len());
self.ptr.rotate_right(n); self.ptr.rotate_right(n);
self.ptr.push_back(m); self.ptr.push_back(m);
} }
} }
} }
fn delta(n: i64, len: i64) -> usize { fn imod(n: i64, m: usize) -> usize {
let n = n.abs(); let n: usize = n.abs().try_into().unwrap();
// It takes n-1 swaps to get back to where we started, so treat these as extra "hops" over the n % m
// original position.
let skips = n / (len - 1);
let extra = n % len;
((skips + extra) % len).try_into().unwrap()
} }