2021: day14: fix stack overflow in part 1
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@ -119,27 +119,41 @@ impl std::str::FromStr for Polymer {
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}
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}
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fn insert_pairs(
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fn insert_pairs(
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mut molecules: LinkedList<char>,
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molecules: LinkedList<char>,
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rules: &HashMap<(char, char), char>,
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rules: &HashMap<(char, char), char>,
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) -> Result<LinkedList<char>> {
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) -> Result<LinkedList<char>> {
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if molecules.len() <= 1 {
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if molecules.len() <= 1 {
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return Ok(molecules);
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return Ok(molecules);
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}
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}
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// List length is at least 2
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let mut head = molecules;
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let mut iter = molecules.iter();
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let mut tail = head.split_off(0);
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let (left, right) = (*iter.next().unwrap(), *iter.next().unwrap());
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let to_insert = *rules
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while tail.len() > 1 {
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.get(&(left, right))
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// List length is at least 2
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.with_context(|| format!("couldn't find rule for pair ({}, {})", left, right))?;
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let mut iter = tail.iter();
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let (left, right) = (*iter.next().unwrap(), *iter.next().unwrap());
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let mut tail = insert_pairs(molecules.split_off(1), rules)?;
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let to_insert = *rules
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.get(&(left, right))
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.with_context(|| format!("couldn't find rule for pair ({}, {})", left, right))?;
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molecules.push_back(to_insert);
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// tail = left
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molecules.append(&mut tail);
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// new_tail = right -> rest
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let new_tail = tail.split_off(1);
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Ok(molecules)
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// head = head -> left
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head.append(&mut tail);
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// head = head -> left -> to_insert
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head.push_back(to_insert);
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// tail = right -> rest
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tail = new_tail;
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}
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head.append(&mut tail);
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Ok(head)
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}
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}
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#[cfg(test)]
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#[cfg(test)]
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