2025/day-06: Solve part 2

2025/rust/day-06/src/main.rs

@@ -1,4 +1,4 @@
-use std::{fmt::Debug, fs};
+use std::{fmt::Debug, fs, str::FromStr};
 
 #[derive(PartialEq, Debug)]
 enum Operation {
@@ -6,6 +6,18 @@ enum Operation {
     Multiply,
 }
 
+impl FromStr for Operation {
+    type Err = ();
+
+    fn from_str(input: &str) -> Result<Operation, Self::Err> {
+        match input {
+            "+" => Ok(Operation::Add),
+            "*" => Ok(Operation::Multiply),
+            _ => Err(()),
+        }
+    }
+}
+
 #[derive(Debug)]
 struct Problem {
     numbers: Vec<u64>,
@@ -14,46 +26,79 @@ struct Problem {
 
 impl Problem {
     fn solve(&self) -> u64 {
-        if self.operation == Operation::Add {
-            self.numbers.iter().sum()
-        } else {
-            self.numbers.iter().product()
+        match self.operation {
+            Operation::Add => self.numbers.iter().sum(),
+            Operation::Multiply => self.numbers.iter().product(),
         }
     }
 }
 
 fn main() {
-    let problems = parse_input(&fs::read_to_string("../../inputs/06.txt").unwrap());
+    let content = &mut fs::read_to_string("../../inputs/06.txt").unwrap();
 
-    println!("Grand total: {}", grand_total(&problems));
+    println!("Grand total 1: {}", grand_total(&parse_input_v1(content)));
+    println!("Grand total 2: {}", grand_total(&parse_input_v2(content)));
 }
 
-fn parse_input(contents: &str) -> Vec<Problem> {
+fn parse_input_v1(contents: &str) -> Vec<Problem> {
     let grid: Vec<Vec<&str>> = contents
         .trim()
         .lines()
         .map(|line| line.split_whitespace().collect())
         .collect();
 
-    let mut list: Vec<Problem> = Vec::new();
+    let operations_row = grid.last().unwrap();
+    let num_cols = grid[0].len();
 
-    for (col, _) in grid[0].iter().enumerate() {
-        let mut numbers: Vec<u64> = Vec::new();
+    (0..num_cols)
+        .map(|col_index| {
+            let operation = Operation::from_str(operations_row[col_index]).unwrap();
 
-        let operation = match grid[grid.len() - 1][col] {
-            "+" => Operation::Add,
-            "*" => Operation::Multiply,
-            _ => panic!("Unsupported Operation"),
-        };
+            let numbers = grid[..grid.len() - 1]
+                .iter()
+                .map(|row| row[col_index].parse().unwrap())
+                .collect();
 
-        for (row, _) in grid[..grid.len() - 1].iter().enumerate() {
-            numbers.push(grid[row][col].parse().unwrap());
+            Problem { numbers, operation }
+        })
+        .collect()
+}
+
+fn parse_input_v2(contents: &str) -> Vec<Problem> {
+    let grid: Vec<Vec<u8>> = contents
+        .trim_end_matches('\n')
+        .lines()
+        .map(|line| line.as_bytes().to_vec())
+        .collect();
+
+    let operations_row = grid.last().unwrap();
+
+    let mut problems = Vec::new();
+
+    let mut numbers = Vec::new();
+    let mut operation = Operation::Add;
+
+    for col in 0..grid[0].len() {
+        if let Ok(op) = Operation::from_str(&(operations_row[col] as char).to_string()) {
+            operation = op;
         }
 
-        list.push(Problem { numbers, operation });
-    }
+        let column: String = (0..grid.len() - 1)
+            .map(|row| grid[row][col] as char)
+            .filter(|c| !c.is_whitespace())
+            .collect();
 
-    list
+        if column.is_empty() {
+            problems.push(Problem { numbers, operation });
+            numbers = Vec::new();
+            operation = Operation::Add;
+        } else {
+            numbers.push(column.parse().unwrap());
+        }
+    }
+    problems.push(Problem { numbers, operation });
+
+    problems
 }
 
 fn grand_total(problems: &[Problem]) -> u64 {
@@ -64,14 +109,19 @@ fn grand_total(problems: &[Problem]) -> u64 {
 mod tests {
     use super::*;
 
-    const TEST_INPUT: &str = "
-123 328  51 64 
+    const TEST_INPUT: &str = "123 328  51 64 
  45 64  387 23 
   6 98  215 314
-*   +   *   +  ";
+*   +   *   +  
+";
 
     #[test]
     fn test_part1() {
-        assert_eq!(grand_total(&parse_input(TEST_INPUT)), 4277556);
+        assert_eq!(grand_total(&parse_input_v1(TEST_INPUT)), 4277556);
+    }
+
+    #[test]
+    fn test_part2() {
+        assert_eq!(grand_total(&parse_input_v2(TEST_INPUT)), 3263827);
     }
 }