From 93af7971e47a6f401eccf02cc7f2b49602a98d17 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hannes=20K=C3=B6rber?= <hannes@hkoerber.de>
Date: Fri, 1 Dec 2023 20:55:29 +0100
Subject: [PATCH] Implement another approach for day 1

---
 2023/1/2/src/main.rs | 204 +++++++++++++++++++++++++++----------------
 1 file changed, 130 insertions(+), 74 deletions(-)

diff --git a/2023/1/2/src/main.rs b/2023/1/2/src/main.rs
index 18fd582..3f79716 100644
--- a/2023/1/2/src/main.rs
+++ b/2023/1/2/src/main.rs
@@ -1,81 +1,137 @@
+#[derive(Debug)]
+struct FirstLast {
+    first: Option<u32>,
+    last: Option<u32>,
+}
+
+impl FirstLast {
+    fn new() -> Self {
+        Self {
+            first: None,
+            last: None,
+        }
+    }
+
+    fn record(&mut self, n: u32) {
+        if self.first.is_none() {
+            self.first = Some(n)
+        } else {
+            self.last = Some(n)
+        }
+    }
+
+    fn value(self) -> u32 {
+        self.first.unwrap() * 10 + self.last.unwrap_or(self.first.unwrap())
+    }
+}
+
+struct SpelledOutNumber(u32);
+
+impl SpelledOutNumber {
+    fn parse(value: &[char]) -> Option<Self> {
+        let value: String = value.into_iter().collect();
+        if value.starts_with("one") {
+            Some(Self(1))
+        } else if value.starts_with("two") {
+            Some(Self(2))
+        } else if value.starts_with("three") {
+            Some(Self(3))
+        } else if value.starts_with("four") {
+            Some(Self(4))
+        } else if value.starts_with("five") {
+            Some(Self(5))
+        } else if value.starts_with("six") {
+            Some(Self(6))
+        } else if value.starts_with("seven") {
+            Some(Self(7))
+        } else if value.starts_with("eight") {
+            Some(Self(8))
+        } else if value.starts_with("nine") {
+            Some(Self(9))
+        } else {
+            None
+        }
+    }
+}
+
 fn main() {
     let input = std::fs::read_to_string("./input").unwrap();
 
-    #[derive(Debug)]
-    struct FirstLast {
-        first: Option<u32>,
-        last: Option<u32>,
-    }
-
-    impl FirstLast {
-        fn new() -> Self {
-            Self {
-                first: None,
-                last: None,
-            }
-        }
-
-        fn record(&mut self, n: u32) {
-            if self.first.is_none() {
-                self.first = Some(n)
-            } else {
-                self.last = Some(n)
-            }
-        }
-
-        fn value(self) -> u32 {
-            self.first.unwrap() * 10 + self.last.unwrap_or(self.first.unwrap())
-        }
-    }
-
-    struct SpelledOutNumber(u32);
-
-    impl SpelledOutNumber {
-        fn parse(value: &str) -> Option<Self> {
-            if value.starts_with("one") {
-                Some(Self(1))
-            } else if value.starts_with("two") {
-                Some(Self(2))
-            } else if value.starts_with("three") {
-                Some(Self(3))
-            } else if value.starts_with("four") {
-                Some(Self(4))
-            } else if value.starts_with("five") {
-                Some(Self(5))
-            } else if value.starts_with("six") {
-                Some(Self(6))
-            } else if value.starts_with("seven") {
-                Some(Self(7))
-            } else if value.starts_with("eight") {
-                Some(Self(8))
-            } else if value.starts_with("nine") {
-                Some(Self(9))
-            } else {
-                None
-            }
-        }
-    }
-
-    let out: u32 = input
-        .lines()
-        .map(|line| {
-            let line: Vec<char> = line.chars().collect();
-            let mut recorder = FirstLast::new();
-            for i in 0..line.len() {
-                let c = &line[i];
-                if let Some(digit) = c.to_digit(10) {
-                    recorder.record(digit)
-                } else {
-                    let rest = &line[i..].iter().collect::<String>();
-                    if let Some(digit) = SpelledOutNumber::parse(rest.as_str()) {
-                        recorder.record(digit.0)
+    let approaches: Vec<u32> = vec![
+        // go through the string one by one, check the value at that position and record it into
+        // a `FirstLast` recorder that holds state
+        input
+            .lines()
+            .map(|line| {
+                let line: Vec<char> = line.chars().collect();
+                let mut recorder = FirstLast::new();
+                for i in 0..line.len() {
+                    let c = &line[i];
+                    if let Some(digit) = c.to_digit(10) {
+                        recorder.record(digit)
+                    } else {
+                        if let Some(digit) = SpelledOutNumber::parse(&line[i..]) {
+                            recorder.record(digit.0)
+                        }
                     }
                 }
-            }
-            recorder
-        })
-        .map(FirstLast::value)
-        .sum();
+                recorder
+            })
+            .map(FirstLast::value)
+            .sum(),
+        //
+        // go through the string one by one, transform it into an array of digits and go from there
+        // i prefer this approach, as there is no stateful iteration
+        input
+            .lines()
+            .map(|line| line.chars().collect::<Vec<char>>())
+            .map(|line| {
+                (0..line.len())
+                    .map(move |pos| {
+                        if let Some(digit) = line[pos].to_digit(10) {
+                            Some(digit)
+                        } else {
+                            SpelledOutNumber::parse(&line[pos..line.len()]).map(|s| s.0)
+                        }
+                    })
+                    .filter_map(|e| e)
+                    .collect::<Vec<u32>>()
+            })
+            // peculiar: if there is only one digit, use it for both the tenths digit and and ones digit
+            .map(|result| (result[0], *result.last().unwrap_or(&result[0])))
+            .map(|(d1, d2)| d1 * 10 + d2)
+            .sum(),
+    ];
 
-    println!("{out}");
+    enum Acc {
+        Init,
+        Some(u32),
+    }
+
+    impl Acc {
+        fn unwrap(self) -> u32 {
+            match self {
+                Self::Init => panic!("Accumulator did not contain a number"),
+                Self::Some(val) => val,
+            }
+        }
+    }
+
+    // check that all approaches result in the same result
+    let result = approaches
+        .iter()
+        // try_reduce would be nicer here
+        .try_fold(Acc::Init, |acc, value| {
+            if let Acc::Some(acc) = acc {
+                if acc != *value {
+                    return Err("approaches give different results");
+                }
+            };
+            Ok(Acc::Some(*value))
+        })
+        .unwrap() // check that there were no different results
+        .unwrap() // check that there were results at all (cannot fail)
+    ;
+
+    println!("{result}");
 }