Modest speed improvements

day_01/src/lib.rs

@@ -1,8 +1,6 @@
-use std::iter::zip;
-
 const WORD_LIST: [&str; 9] = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"];
-// const REVERSE_WORD_LIST: [&str; 9] = ["eno", "owt", "eerht", "ruof", "evif", "xis", "neves", "thgie", "enin"];
-const DIGIT_LIST: [&str; 9] = ["o1e", "t2o", "t3e", "f4r", "f5e", "s6x", "s7n", "e8t", "n9e"];
+const REVERSE_WORD_LIST: [&str; 9] = ["eno", "owt", "eerht", "ruof", "evif", "xis", "neves", "thgie", "enin"];
+const DIGIT_LIST: [u32; 9] = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 
 fn find_first_digit(line: &str) -> u32 {
     match line.chars().find(|character| { character.is_digit(10) }) {
@@ -18,12 +16,52 @@ fn find_last_digit(line: &str) -> u32 {
     }
 }
 
-fn replace_with_digits(input: &str) -> String {
-    let mut output = input.to_string();
-    for (word, digit) in zip(WORD_LIST, DIGIT_LIST) {
-        output = output.replace(word, digit).to_string();
+fn contains_digit_or_spelled(subline: &str) -> Option<u32> {
+    if subline.starts_with(WORD_LIST[0]) {
+        return Some(DIGIT_LIST[0]);
+    } else if subline.starts_with(WORD_LIST[1]) {
+        return Some(DIGIT_LIST[1]);
+    } else if subline.starts_with(WORD_LIST[2]) {
+        return Some(DIGIT_LIST[2]);
+    } else if subline.starts_with(WORD_LIST[3]) {
+        return Some(DIGIT_LIST[3]);
+    } else if subline.starts_with(WORD_LIST[4]) {
+        return Some(DIGIT_LIST[4]);
+    } else if subline.starts_with(WORD_LIST[5]) {
+        return Some(DIGIT_LIST[5]);
+    } else if subline.starts_with(WORD_LIST[6]) {
+        return Some(DIGIT_LIST[6]);
+    } else if subline.starts_with(WORD_LIST[7]) {
+        return Some(DIGIT_LIST[7]);
+    } else if subline.starts_with(WORD_LIST[8]) {
+        return Some(DIGIT_LIST[8]);
+    } else {
+        subline.chars().next().unwrap().to_digit(10)
+    }
+}
+
+fn contains_digit_or_spelled_reverse(subline: &str) -> Option<u32> {
+    if subline.starts_with(REVERSE_WORD_LIST[0]) {
+        return Some(DIGIT_LIST[0]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[1]) {
+        return Some(DIGIT_LIST[1]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[2]) {
+        return Some(DIGIT_LIST[2]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[3]) {
+        return Some(DIGIT_LIST[3]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[4]) {
+        return Some(DIGIT_LIST[4]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[5]) {
+        return Some(DIGIT_LIST[5]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[6]) {
+        return Some(DIGIT_LIST[6]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[7]) {
+        return Some(DIGIT_LIST[7]);
+    } else if subline.starts_with(REVERSE_WORD_LIST[8]) {
+        return Some(DIGIT_LIST[8]);
+    } else {
+        subline.chars().next().unwrap().to_digit(10)
     }
-    output
 }
 
 pub fn part1(input: &str) -> String {
@@ -39,8 +77,28 @@ pub fn part1(input: &str) -> String {
 }
 
 pub fn part2(input: &str) -> String {
-    let parsed_inputs = &replace_with_digits(input);
-    part1(parsed_inputs)
+    let calibration_lines = input
+        .lines()
+        .map(|line| {
+            let mut first = 0;
+            for i in 0..line.len() {
+                if let Some(i) = contains_digit_or_spelled(&line[i..]) {
+                    first = i;
+                    break;
+                }
+            };
+            let reversed_line = line.chars().rev().collect::<String>();
+            let mut last = 0;
+            for i in 0..line.len() {
+                if let Some(i) = contains_digit_or_spelled_reverse(&reversed_line[i..]) {
+                    last = i;
+                    break;
+                }
+            };
+            format!("{}{}", first, last).parse::<u32>().unwrap()
+        })
+        .collect::<Vec<_>>();
+    format!("{}", calibration_lines.into_iter().sum::<u32>())
 }
 
 pub mod prelude {