y2024d3p2

y2024/src/days/d3.rs

@@ -25,33 +25,64 @@ fn extract_mul_pairs(line: &str) -> Vec<(i32, i32)> {
         .collect::<Vec<(i32, i32)>>()
 }
 
-fn remove_donts(line: &str) -> String {
-    let mut new_line = line.to_string();
-    loop {
-        println!("len {}", line.len());
-        let mut end_range = new_line.len() - 1;
-        if let Some(dont_idx) = new_line.find("don't()") {
-            if let Some(do_idx) = new_line.find("do()") {
-                if dont_idx < do_idx {
-                    end_range = do_idx + 4;
+fn extract_mul_pairs_dont(line: &str) -> Vec<(i32, i32)> {
+    let mut pairs = Vec::new();
+    for (idx, _) in line.match_indices("mul(") {
+        if let Some(dont_func) = line[..idx].rfind("don't()") {
+            if let Some(do_func) = line[..idx].rfind("do()") {
+                if do_func < dont_func {
+                    continue;
                 }
+            } else {
+                continue;
             }
-            println!("dont {dont_idx} to {end_range}");
-            new_line.replace_range(dont_idx..end_range, "");
-        } else {
-            return new_line;
+        }
+        let mut invalid = false;
+        let mut comma_pos = 0;
+        let mut pair = ("".to_string(), "".to_string());
+        // max length of parenthesis == 9
+        for paren_idx in 0..9 {
+            let paren_content = match line.as_bytes().get(idx + 4 + paren_idx) {
+                Some(content) => *content as char,
+                None => {
+                    invalid = true;
+                    break;
+                }
+            };
+            if paren_content == ')' {
+                if comma_pos == 0 {
+                    invalid = true;
+                }
+                break;
+            }
+            if paren_content == ',' {
+                comma_pos = paren_idx;
+                continue;
+            }
+            if !paren_content.is_ascii_digit() {
+                invalid = true;
+                break;
+            }
+            if comma_pos == 0 {
+                pair.0.push(paren_content);
+            } else {
+                pair.1.push(paren_content);
+            }
+        }
+        if !invalid {
+            let a = pair.0.parse::<i32>().unwrap();
+            let b = pair.1.parse::<i32>().unwrap();
+            pairs.push((a, b));
         }
     }
+    pairs
 }
 
 pub fn process_part2(input: &str) -> i32 {
-    input
-        .lines()
-        .map(|line| {
-            let line = remove_donts(line);
-            extract_mul_pairs(&line)
-        })
-        .map(|pairs| pairs.iter().map(|(a, b)| a * b).sum::<i32>())
+    let input = input.lines().collect::<Vec<&str>>().join("");
+    extract_mul_pairs_dont(&input)
+        .into_iter()
+        .map(|(a, b)| a * b)
         .sum()
 }
 
@@ -86,4 +117,12 @@ mod tests {
         let result = process_part2(INPUT_2);
         assert_eq!(result, 48);
     }
+
+    #[test]
+    fn res2() {
+        let root = env!("CARGO_MANIFEST_DIR");
+        let content = fs::read_to_string(format!("{root}/resources/3_input.txt")).unwrap();
+        let result = process_part2(&content);
+        assert_eq!(result, 62098619);
+    }
 }