Add another approach, make setup more elegant
This commit is contained in:
@@ -1,29 +1,4 @@
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#[derive(Debug)]
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struct NumberPair(Option<u32>, Option<u32>);
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struct FirstLast {
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first: Option<u32>,
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last: Option<u32>,
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}
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impl FirstLast {
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fn new() -> Self {
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Self {
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first: None,
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last: None,
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}
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}
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fn record(&mut self, n: u32) {
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if self.first.is_none() {
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self.first = Some(n)
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} else {
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self.last = Some(n)
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}
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}
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fn value(self) -> u32 {
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self.first.unwrap() * 10 + self.last.unwrap_or(self.first.unwrap())
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}
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}
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struct SpelledOutNumber(u32);
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struct SpelledOutNumber(u32);
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@@ -54,84 +29,143 @@ impl SpelledOutNumber {
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}
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}
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}
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}
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fn try_parse_at(input: &[char]) -> Option<u32> {
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if let Some(digit) = input[0].to_digit(10) {
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Some(digit)
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} else {
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SpelledOutNumber::parse(&input[0..input.len()]).map(|s| s.0)
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}
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}
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fn main() {
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fn main() {
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let input = std::fs::read_to_string("./input").unwrap();
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let input = std::fs::read_to_string("./input").unwrap();
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let approaches: Vec<u32> = vec![
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let approaches: Vec<Box<dyn Fn(&[char]) -> NumberPair>> = vec![
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// go through the string one by one, check the value at that position and record it into
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// go through the string one by one, check the value at that position and record it into
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// a `FirstLast` recorder that holds state
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// a `FirstLast` recorder that holds state
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input
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Box::new(|line| {
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.lines()
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#[derive(Debug)]
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.map(|line| {
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struct Recorder {
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let line: Vec<char> = line.chars().collect();
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first: Option<u32>,
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let mut recorder = FirstLast::new();
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last: Option<u32>,
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for i in 0..line.len() {
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}
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let c = &line[i];
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if let Some(digit) = c.to_digit(10) {
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impl Recorder {
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recorder.record(digit)
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fn new() -> Self {
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} else {
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Self {
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if let Some(digit) = SpelledOutNumber::parse(&line[i..]) {
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first: None,
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recorder.record(digit.0)
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last: None,
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}
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}
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}
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}
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}
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recorder
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})
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fn record(&mut self, n: u32) {
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.map(FirstLast::value)
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if self.first.is_none() {
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.sum(),
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self.first = Some(n)
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} else {
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self.last = Some(n)
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}
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}
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fn finish(self) -> NumberPair {
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NumberPair(self.first, self.last)
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}
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}
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let mut recorder = Recorder::new();
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for i in 0..line.len() {
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let c = &line[i];
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if let Some(digit) = c.to_digit(10) {
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recorder.record(digit)
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} else {
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if let Some(digit) = SpelledOutNumber::parse(&line[i..]) {
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recorder.record(digit.0)
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}
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}
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}
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recorder.finish()
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}),
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//
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//
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// go through the string one by one, transform it into an array of digits and go from there
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// Go through the string one by one, transform it into an array of digits and go from there
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// i prefer this approach, as there is no stateful iteration
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// I prefer this approach, as there is no stateful iteration and it's very easy to understand
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input
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Box::new(|line| {
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.lines()
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let result = (0..line.len())
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.map(|line| line.chars().collect::<Vec<char>>())
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.map(move |pos| try_parse_at(&line[pos..line.len()]))
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.map(|line| {
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// remove none values
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(0..line.len())
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.filter_map(|e| e)
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.map(move |pos| {
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.collect::<Vec<u32>>();
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if let Some(digit) = line[pos].to_digit(10) {
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Some(digit)
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} else {
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SpelledOutNumber::parse(&line[pos..line.len()]).map(|s| s.0)
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}
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})
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.filter_map(|e| e)
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.collect::<Vec<u32>>()
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})
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// peculiar: if there is only one digit, use it for both the tenths digit and and ones digit
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// peculiar: if there is only one digit, use it for both the tenths digit and and ones digit
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.map(|result| (result[0], *result.last().unwrap_or(&result[0])))
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NumberPair(result.get(0).copied(), result.last().copied())
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.map(|(d1, d2)| d1 * 10 + d2)
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}),
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.sum(),
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//
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// this one does two scans, one from each end. it's elegant because it does not require special
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// handling for lines containing only one digit, i.e. it will *always* return (Some, Some)
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Box::new(|line| {
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NumberPair(
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{
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let mut tenth = None;
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for pos in 0..line.len() {
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if let Some(digit) = try_parse_at(&line[pos..line.len()]) {
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tenth = Some(digit);
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break;
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}
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}
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tenth
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},
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{
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let mut ones = None;
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for pos in (0..line.len()).rev() {
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if let Some(digit) = try_parse_at(&line[pos..line.len()]) {
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ones = Some(digit);
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break;
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}
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}
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ones
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},
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)
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}),
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];
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];
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enum Acc {
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let result: u32 = input
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Init,
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.lines()
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Some(u32),
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.map(|line| line.chars().collect::<Vec<char>>())
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}
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.map(|line| {
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(
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impl Acc {
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approaches
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fn unwrap(self) -> u32 {
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.iter()
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match self {
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.map(|approach| approach(&line))
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Self::Init => panic!("Accumulator did not contain a number"),
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.map(|pair| {
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Self::Some(val) => val,
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(
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}
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// we assume that there will *always* at least be one numbers in there
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}
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pair.0.unwrap(),
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}
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// if there is no second number, we "reuse" the first. so "7" => 77
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pair.1.or(pair.0).unwrap(),
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// check that all approaches result in the same result
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)
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let result = approaches
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})
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.iter()
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.collect::<Vec<(u32, u32)>>(),
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// try_reduce would be nicer here
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line,
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.try_fold(Acc::Init, |acc, value| {
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)
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if let Acc::Some(acc) = acc {
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if acc != *value {
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return Err("approaches give different results");
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}
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};
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Ok(Acc::Some(*value))
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})
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})
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.unwrap() // check that there were no different results
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.map(|(results, line)| {
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.unwrap() // check that there were results at all (cannot fail)
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// check that all approaches result in the same result
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;
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let result = results[0];
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let mut all_agree = true;
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for other_result in &results[1..] {
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if *other_result != result {
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all_agree = false;
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}
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}
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if !all_agree {
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eprintln!("approaches yield different results!");
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eprintln!("input: {}", line.iter().collect::<String>());
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eprintln!("results: {results:?}");
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}
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results[0]
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})
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.map(|(tenth, ones)| tenth * 10 + ones)
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.sum();
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println!("{result}");
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println!("{result}");
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}
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}
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