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2021: day14: fix stack overflow in part 1

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This commit is contained in:
Antoine Martin 2021-12-14 13:39:48 +01:00
parent 218d9d5298
commit 9d81739f2b
1 changed files with 25 additions and 11 deletions
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36
aoc2021/src/day14.rs
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@ -119,27 +119,41 @@ impl std::str::FromStr for Polymer {
}
fn insert_pairs(
mut molecules: LinkedList<char>,
molecules: LinkedList<char>,
rules: &HashMap<(char, char), char>,
) -> Result<LinkedList<char>> {
if molecules.len() <= 1 {
return Ok(molecules);
}
// List length is at least 2
let mut iter = molecules.iter();
let (left, right) = (*iter.next().unwrap(), *iter.next().unwrap());
let mut head = molecules;
let mut tail = head.split_off(0);
let to_insert = *rules
.get(&(left, right))
.with_context(|| format!("couldn't find rule for pair ({}, {})", left, right))?;
while tail.len() > 1 {
// List length is at least 2
let mut iter = tail.iter();
let (left, right) = (*iter.next().unwrap(), *iter.next().unwrap());
let mut tail = insert_pairs(molecules.split_off(1), rules)?;
let to_insert = *rules
.get(&(left, right))
.with_context(|| format!("couldn't find rule for pair ({}, {})", left, right))?;
molecules.push_back(to_insert);
molecules.append(&mut tail);
// tail = left
// new_tail = right -> rest
let new_tail = tail.split_off(1);
Ok(molecules)
// head = head -> left
head.append(&mut tail);
// head = head -> left -> to_insert
head.push_back(to_insert);
// tail = right -> rest
tail = new_tail;
}
head.append(&mut tail);
Ok(head)
}
#[cfg(test)]