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retroactive, to derust my rust
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137pub fn day9_part1(input: &str) -> String { let diskmap = parse(input); let mut blocks = diskmap_to_blocks(&diskmap); compact(&mut blocks); let sum = checksum(&blocks); sum.to_string()}
pub fn day9_part2(input: &str) -> String { let diskmap = parse(input); let compacted_diskmap = defrag_compact(&diskmap); let blocks = compacted_diskmap_to_blocks(&compacted_diskmap); let sum = checksum(&blocks); sum.to_string()}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]struct File { id: u64, length: usize, free_space: usize,}
fn compacted_diskmap_to_blocks(compacted_diskmap: &[File]) -> Vec<Option<u64>> { compacted_diskmap .iter() .flat_map(|file| { [ vec![Some(file.id); file.length], vec![None; file.free_space], ] }) .flatten() .collect()}
fn defrag_compact(diskmap: &[usize]) -> Vec<File> { let files = diskmap_to_files(diskmap); let mut compacted_files = files.clone();
for file in files.clone().into_iter().rev() { let Some(insertable_index) = compacted_files .iter() .enumerate() .find(|(_, insertable_file)| insertable_file.free_space >= file.length) .map(|(i, _)| i) else { continue; };
let prev_free_space = compacted_files[insertable_index].free_space; compacted_files[insertable_index].free_space = 0; compacted_files.insert(insertable_index + 1, file); compacted_files[insertable_index + 1].free_space = prev_free_space - file.length;
let nullable_index = compacted_files .iter() .enumerate() .rev() .find(|(_, nullable_file)| nullable_file.id == file.id) .map(|(i, _)| i) .unwrap(); compacted_files[nullable_index - 1].free_space += compacted_files[nullable_index].length + compacted_files[nullable_index].free_space; compacted_files.remove(nullable_index); }
compacted_files}
fn diskmap_to_files(diskmap: &[usize]) -> Vec<File> { let mut id = 0u64; let mut blocks = vec![];
for digit in diskmap { if id % 2 == 0 { blocks.push(File { id: id / 2, length: *digit, free_space: 0, }); } else { blocks.last_mut().unwrap().free_space = *digit; } id += 1 }
blocks}
fn checksum(blocks: &[Option<u64>]) -> u64 { blocks .iter() .enumerate() .map(|(index, block)| if let Some(block) = block {index as u64 * block} else {0}) .sum::<u64>()}
fn diskmap_to_blocks(diskmap: &[usize]) -> Vec<Option<u64>> { let mut id = 0u64; let mut blocks = vec![];
for digit in diskmap { if id % 2 == 0 { blocks.extend_from_slice(&vec![Some(id / 2); *digit]); } else { blocks.extend_from_slice(&vec![None; *digit]); } id += 1 }
blocks}
fn compact(blocks: &mut [Option<u64>]) { let mut start_index = 0; let mut end_index = blocks.len() - 1;
while start_index < end_index { if blocks[start_index].is_some() { start_index += 1; } else if blocks[end_index].is_none() { end_index -= 1 } else { blocks[start_index] = blocks[end_index]; blocks[end_index] = None; } }}
fn parse(input: &str) -> Vec<usize> { input .chars() .map(|char| char.to_digit(10).unwrap() as usize) .collect()}