2021: day08: only store "hard" digits in mapping
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@ -65,21 +65,20 @@ impl<'a> Entry<'a> {
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let mut mapping = Vec::new();
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// first, let's get the easy digits
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self.unique_signals
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let easy_digits: Vec<(&str, u64)> = self
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.unique_signals
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.iter()
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.filter_map(|signal| Self::translate_easy_digit(signal).zip(Some(signal)))
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.for_each(|(translation, &signal)| {
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mapping.push((signal, translation));
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});
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.filter_map(|signal| Some(*signal).zip(Self::translate_easy_digit(signal)))
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.collect();
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// now we can get `9` for free: it's the signal that uses 6 segments and has 4 in common
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// with the digit `4` (`6` and `0` also use 6 segments, but only have 3 segments in common
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// with `4`).
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let (four, _) = *mapping
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let (four, _) = *easy_digits
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.iter()
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.find(|(_, translation)| *translation == 4)
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.context("no signal found for the digit 4!")?;
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let nine = self
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let nine = *self
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 6)
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@ -88,32 +87,32 @@ impl<'a> Entry<'a> {
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mapping.push((nine, 9));
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// `0` has 2 segments in common with `1`, while `6` only has 1.
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let (one, _) = *mapping
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let (one, _) = *easy_digits
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.iter()
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.find(|(_, translation)| *translation == 1)
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.context("no signal found for the digit 1!")?;
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let zero = self
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let zero = *self
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 6)
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.filter(|signal| *signal != nine)
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.filter(|&signal| signal.len() == 6)
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.filter(|&signal| *signal != nine)
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.find(|signal| one.chars().all(|c| signal.contains(c)))
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.context("couldn't identify any signal corresponding to the digit 0!")?;
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mapping.push((zero, 0));
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// `6` is an easy one now, the only other signal with 6 segments, that isn't nine or zero.
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let six = self
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let six = *self
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 6)
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.find(|signal| *signal != nine && *signal != zero)
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.find(|&signal| *signal != nine && *signal != zero)
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.context("couldn't identify any signal corresponding to the digit 6!")?;
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mapping.push((six, 6));
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// `2`, `3` and `5` have 5 segments each.
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//
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// `3` has 2 segments in common with `1`.
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let three = self
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let three = *self
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 5)
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@ -122,7 +121,7 @@ impl<'a> Entry<'a> {
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mapping.push((three, 3));
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// `5` has all its segments used in `6`, `2` doesn't.
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let five = self
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let five = *self
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 5)
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@ -135,11 +134,11 @@ impl<'a> Entry<'a> {
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.unique_signals
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.iter()
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.filter(|signal| signal.len() == 5)
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.find(|signal| *signal != five && *signal != three)
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.find(|&signal| *signal != five && *signal != three)
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.context("couldn't identify any signal corresponding to the digit 2!")?;
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mapping.push((two, 2));
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debug_assert_eq!(mapping.len(), 10);
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debug_assert_eq!(mapping.len(), 6);
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Ok(mapping)
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}
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@ -149,16 +148,21 @@ impl<'a> Entry<'a> {
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for digit in &self.four_digits_output {
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// search is kind of ugly, but having to sort everything is probably time consuming as
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// well.
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let digit = digit_mapping
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.iter()
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.find_map(|(signal, translation)| {
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if digit.len() == signal.len() && digit.chars().all(|c| signal.contains(c)) {
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Some(translation)
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} else {
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None
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}
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})
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.with_context(|| format!("couldn't translate digit `{}`", digit))?;
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let digit = if let Some(translation) = Self::translate_easy_digit(digit) {
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translation
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} else {
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*digit_mapping
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.iter()
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.find_map(|(signal, translation)| {
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if digit.len() == signal.len() && digit.chars().all(|c| signal.contains(c))
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{
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Some(translation)
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} else {
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None
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}
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})
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.with_context(|| format!("couldn't translate digit `{}`", digit))?
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};
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res = (res * 10) + digit;
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}
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