45 lines
1.2 KiB
Rust
45 lines
1.2 KiB
Rust
pub fn day7() {
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// let input = "16,1,2,0,4,2,7,1,2,14";
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let input = include_str!("../input/day7.txt");
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let horiz_positions = input
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.trim()
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.split(",")
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.map(|s| s.parse::<i32>().unwrap())
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.collect::<Vec<_>>();
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let candidates =
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*horiz_positions.iter().min().unwrap()..=*horiz_positions.iter().max().unwrap();
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let min = candidates
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.clone()
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.min_by_key(|pos| cost_to_align_at(pos, &horiz_positions));
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println!("target position: {:?}", min);
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println!(
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"fuel cost: {:?}",
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cost_to_align_at(&min.unwrap(), &horiz_positions)
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);
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let p2_min = candidates.min_by_key(|pos| p2_cost(pos, &horiz_positions));
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println!("p2 target position: {:?}", p2_min);
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println!(
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"p2 fuel cost: {:?}",
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p2_cost(&p2_min.unwrap(), &horiz_positions)
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);
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}
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fn cost_to_align_at(target: &i32, horiz_positions: &[i32]) -> i32 {
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horiz_positions.iter().map(|pos| (pos - target).abs()).sum()
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}
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fn p2_cost(target: &i32, horiz_positions: &[i32]) -> i32 {
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horiz_positions
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.iter()
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.map(|pos| {
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let max = (pos - target).abs();
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// thanks, Gauss
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(max * (max + 1)) / 2
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})
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.sum()
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}
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