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fn main() {
let input : Vec<i32> = advent::read_file(7).trim_end()
.split_terminator(',')
.map(|n| n.parse::<i32>().unwrap())
.collect();
println!("7a: {}", least_fuel(&input));
println!("7b: {}", least_crab_fuel(&input));
}
fn least_fuel(positions: &[i32]) -> i32 {
let min_pos = *positions.iter().min().unwrap();
let max_pos = *positions.iter().max().unwrap();
(min_pos ..= max_pos).map(|pos| fuel_at_pos(positions, pos))
.min()
.unwrap()
}
fn fuel_at_pos(positions: &[i32], dest: i32) -> i32 {
positions.iter()
.map(|pos| (pos - dest).abs())
.sum()
}
fn least_crab_fuel(positions: &[i32]) -> i32 {
let min_pos = *positions.iter().min().unwrap();
let max_pos = *positions.iter().max().unwrap();
(min_pos ..= max_pos).map(|pos| crab_fuel_at_pos(positions, pos))
.min()
.unwrap()
}
fn gauss_sum(n: i32) -> i32 {
n * (n + 1) / 2
}
fn crab_fuel_at_pos(positions: &[i32], dest: i32) -> i32 {
positions.iter()
.map(|pos| gauss_sum((pos - dest).abs()))
.sum()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let positions = [16,1,2,0,4,2,7,1,2,14];
assert_eq!(fuel_at_pos(&positions, 2), 37);
assert_eq!(fuel_at_pos(&positions, 1), 41);
assert_eq!(fuel_at_pos(&positions, 3), 39);
assert_eq!(fuel_at_pos(&positions, 10), 71);
assert_eq!(least_fuel(&positions), 37);
assert_eq!(crab_fuel_at_pos(&positions, 2), 206);
assert_eq!(least_crab_fuel(&positions), 168);
}
}
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