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use std::fs;
use std::path::Path;
/* AOC21 Day 9: https://adventofcode.com/2021/day/9 */
fn main() {
let input = Path::new("resources").join("input.txt");
let content = fs::read_to_string(input).expect("Unable to read input file");
let width = content.lines().next().expect("Empty input").len();
let heightmap: Vec<u8> = content.lines().flat_map(|l| l.bytes().map(|c| c-b'0')).collect();
println!("Ex1: The risk level is {}", risk_level(&heightmap, width));
println!("Ex2: The result is {}", find_basins(&heightmap, width));
}
fn risk_level(hm: &[u8], w: usize) -> u32 {
(0..hm.len()).map(|i|
if ( i < w || hm[i-w] > hm[i] ) &&
( i+w >= hm.len() || hm[i+w] > hm[i] ) &&
( i%w == 0 || hm[i-1] > hm[i] ) &&
( (i+1)%w == 0 || hm[i+1] > hm[i] ) {
1 + hm[i] as u32
} else { 0 }
).sum()
}
fn find_basins(hm: &[u8], w: usize) -> u32 {
let mut hmask = vec![false;hm.len()];
let mut basins: Vec<u32> = vec![];
for i in 0..hm.len() {
let size = propagate_basin(hm, &mut hmask, i, w);
if size > 0 { basins.push(size); }
}
basins.sort_by(|a,b| b.cmp(a));
basins.iter().take(3).product()
}
fn propagate_basin(hm: &[u8], hmask: &mut [bool], i: usize, w: usize) -> u32 {
if !hmask[i] && hm[i] != 9 {
hmask[i] = true;
1 + if i >= w { propagate_basin(hm, hmask, i-w, w) } else { 0 } +
if i+w < hm.len() { propagate_basin(hm, hmask, i+w, w) } else { 0 } +
if i%w != 0 { propagate_basin(hm, hmask, i-1, w) } else { 0 } +
if (i+1)%w != 0 { propagate_basin(hm, hmask, i+1, w) } else { 0 }
} else {
0
}
}
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