From 2af5f34f1ec4a01f1d08b2278330f422b00f4b5e Mon Sep 17 00:00:00 2001
From: Reiner Herrmann <reiner@reiner-h.de>
Date: Fri, 1 Dec 2023 12:34:19 +0100
Subject: day1 solution 2

---
 src/bin/day1.rs | 56 +++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 45 insertions(+), 11 deletions(-)

(limited to 'src')

diff --git a/src/bin/day1.rs b/src/bin/day1.rs
index 4784496..ec4c2bc 100644
--- a/src/bin/day1.rs
+++ b/src/bin/day1.rs
@@ -2,20 +2,43 @@ static DAY: u8 = 1;
 
 fn main() {
     let input = advent::read_lines(DAY);
-    println!("{DAY}a: {}", sum_digits(&input));
-    println!("{DAY}b: {}", 0);
+    println!("{DAY}a: {}", sum_digits(&input, false));
+    println!("{DAY}b: {}", sum_digits(&input, true));
 }
 
-fn sum_digits(input: &[String]) -> u32 {
+fn starts_with_number(word: &str, consider_words: bool) -> Option<u32> {
+    if let Some(digit) = word.chars().next().unwrap().to_digit(10) {
+        return Some(digit);
+    }
+    if !consider_words {
+        return None
+    }
+    let digits = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"];
+    for (pos, digit) in digits.iter().enumerate() {
+        if word.starts_with(digit) {
+            return Some(pos as u32 + 1);
+        }
+    }
+    None
+}
+
+fn sum_digits(input: &[String], consider_words: bool) -> u32 {
     let mut sum = 0;
     for line in input {
-        let left_pos = line.find(|c: char| c.is_digit(10)).expect("line contains digit");
-        let right_pos = line.rfind(|c: char| c.is_digit(10)).expect("line contains digit");
-
-        let line = line.as_bytes();
-        let left_digit = (line[left_pos] as char).to_digit(10).unwrap();
-        let right_digit = (line[right_pos] as char).to_digit(10).unwrap();
-        sum += (left_digit * 10 + right_digit) as u32;
+        let mut line_number = 0;
+        for pos in 0 .. line.len() {
+            if let Some(number) = starts_with_number(&line[pos..], consider_words) {
+                line_number += 10 * number;
+                break;
+            }
+        }
+        for pos in (0 .. line.len()).rev() {
+            if let Some(number) = starts_with_number(&line[pos..], consider_words) {
+                line_number += number;
+                break;
+            }
+        }
+        sum += line_number;
     }
     sum
 }
@@ -32,6 +55,17 @@ mod tests {
             "a1b2c3d4e5f",
             "treb7uchet",
         ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
-        assert_eq!(sum_digits(&input), 142);
+        assert_eq!(sum_digits(&input, false), 142);
+
+        let input = [
+            "two1nine",
+            "eightwothree",
+            "abcone2threexyz",
+            "xtwone3four",
+            "4nineeightseven2",
+            "zoneight234",
+            "7pqrstsixteen",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+        assert_eq!(sum_digits(&input, true), 281);
     }
 }
-- 
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