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Simplify y-hit iterator

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Bert Peters
2021-12-18 18:12:41 +01:00
parent 101ebee505
commit 6506af879a
1 changed files with 3 additions and 3 deletions
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6
2021/src/day17.rs
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@@ -36,18 +36,18 @@ fn find_hit(initial: i32, range: &RangeInclusive<i32>) -> impl Iterator<Item = i
// to hit, find x := (max(box) + min(box)) / 2 = f(x) // to hit, find x := (max(box) + min(box)) / 2 = f(x)
// = -1/2x^2 + (initial + 0.5)x // = -1/2x^2 + (initial + 0.5)x
// -1/2x^2 + (initial + 0.5)x - (max(box) + min(box)) / 2 = 0 // -1/2x^2 + (initial + 0.5)x - (max(box) + min(box)) / 2 = 0
let middle = (*range.start() + *range.end()) as f64 / 2.; let middle = *range.start() as f64;
let b = initial as f64 + 0.5; let b = initial as f64 + 0.5;
let hit = if let Some(hit) = solve_quadratic(-0.5, b, -middle) { let hit = if let Some(hit) = solve_quadratic(-0.5, b, -middle) {
hit as i32 hit as i32
} else { } else {
// Cause an empty range
-1 -1
}; };
(0..=hit) (0..=hit)
.rev() .rev()
.take_while(move |&n| range.contains(&position(initial, n))) .take_while(move |&n| range.contains(&position(initial, n)))
.chain(((hit + 1)..).take_while(move |&n| range.contains(&position(initial, n))))
} }
fn find_speed(x: i32, range: &RangeInclusive<i32>) -> Option<(i32, i32)> { fn find_speed(x: i32, range: &RangeInclusive<i32>) -> Option<(i32, i32)> {
@@ -135,7 +135,7 @@ mod tests {
fn test_find_hit() { fn test_find_hit() {
assert_eq!(find_hit(2, &(-10..=-5)).collect::<Vec<_>>(), vec![7]); assert_eq!(find_hit(2, &(-10..=-5)).collect::<Vec<_>>(), vec![7]);
assert_eq!(find_hit(3, &(-10..=-5)).collect::<Vec<_>>(), vec![9]); assert_eq!(find_hit(3, &(-10..=-5)).collect::<Vec<_>>(), vec![9]);
assert_eq!(find_hit(0, &(-10..=-5)).collect::<Vec<_>>(), vec![4, 5]); assert_eq!(find_hit(0, &(-10..=-5)).collect::<Vec<_>>(), vec![5, 4]);
} }
#[test] #[test]