day6: problem 2 solution

6/src/main.rs

@@ -102,6 +102,8 @@ fn main() {
 // PARSER
 
 #[derive(Debug)]
+
+// Appropriate for Problem 1 only
 struct Races(Vec<(u64, u64)>);
 
 impl<T: BufRead> From<Lines<T>> for Races {
@@ -152,12 +154,47 @@ fn problem1_possible_wins(race: (u64, u64)) -> u64 {
 
 fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
     let races = Races::from(input);
-    races.0.iter().map(|race| problem1_possible_wins(*race)).fold(1, |accum, elem| accum * elem)
+    races
+        .0
+        .iter()
+        .map(|race| problem1_possible_wins(*race))
+        .fold(1, |accum, elem| accum * elem)
 }
 
 // PROBLEM 2 solution
-fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
-    0
+
+// As the race is about to start, you realize the piece of paper with race times and
+// record distances you got earlier actually just has very bad kerning. There's really
+// only one race - ignore the spaces between the numbers on each line.
+
+// So, the example from before:
+
+// Time:      7  15   30
+// Distance:  9  40  200
+
+// ...now instead means this:
+
+// Time:      71530
+// Distance:  940200
+
+// Now, you have to figure out how many ways there are to win this single race. In this
+// example, the race lasts for 71530 milliseconds and the record distance you need to
+// beat is 940200 millimeters. You could hold the button anywhere from 14 to 71516
+// milliseconds and beat the record, a total of 71503 ways!
+
+// How many ways can you beat the record in this one much longer race?
+
+fn problem2_parse_all_digits_to_number(s: &str) -> u64 {
+    s.chars().filter(|c| c.is_digit(10)).fold(0, |accum, elem| {
+        accum * 10 + elem.to_digit(10).unwrap() as u64
+    })
+}
+
+fn problem2<T: BufRead>(mut input: Lines<T>) -> u64 {
+    let time = problem2_parse_all_digits_to_number(input.next().unwrap().unwrap().as_str());
+    let distance = problem2_parse_all_digits_to_number(input.next().unwrap().unwrap().as_str());
+
+    problem1_possible_wins((time, distance))
 }
 
 #[cfg(test)]
@@ -186,9 +223,9 @@ Distance:  9  40  200";
 
     #[test]
     fn test_possible_wins() {
-        assert_eq!(problem1_possible_wins((7,9)), 4);
-        assert_eq!(problem1_possible_wins((15,40)), 8);
-        assert_eq!(problem1_possible_wins((30,200)), 9);
+        assert_eq!(problem1_possible_wins((7, 9)), 4);
+        assert_eq!(problem1_possible_wins((15, 40)), 8);
+        assert_eq!(problem1_possible_wins((30, 200)), 9);
     }
 
     #[test]
@@ -196,4 +233,10 @@ Distance:  9  40  200";
         let c = Cursor::new(EXAMPLE);
         assert_eq!(problem1(c.lines()), 288);
     }
+
+    #[test]
+    fn test_problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 71503);
+    }
 }