day 10

Author: erning

inputs/10-example.txt

@@ -0,0 +1,31 @@
+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3

inputs/10-input.txt

@@ -0,0 +1,92 @@
+56
+139
+42
+28
+3
+87
+142
+57
+147
+6
+117
+95
+2
+112
+107
+54
+146
+104
+40
+26
+136
+127
+111
+47
+8
+24
+13
+92
+18
+130
+141
+37
+81
+148
+31
+62
+50
+80
+91
+33
+77
+1
+96
+100
+9
+120
+27
+97
+60
+102
+25
+83
+55
+118
+19
+113
+49
+133
+14
+119
+88
+124
+110
+145
+65
+21
+7
+74
+72
+61
+103
+20
+41
+53
+32
+44
+10
+34
+121
+114
+67
+69
+66
+82
+101
+68
+84
+48
+73
+17
+43
+140

src/day10.rs

@@ -0,0 +1,48 @@
+fn parse_input(input: &str) -> Vec<i32> {
+    input.trim().lines().map(|s| s.parse().unwrap()).collect()
+}
+
+pub fn part_one(input: &str) -> usize {
+    let mut input = parse_input(input);
+    input.push(0);
+    input.sort_unstable();
+    input.push(input.last().unwrap() + 3);
+    let diffs: Vec<i32> = input.windows(2).map(|v| v[1] - v[0]).collect();
+    let c1 = diffs.iter().filter(|&v| *v == 1).count();
+    let c3 = diffs.iter().filter(|&v| *v == 3).count();
+    c1 * c3
+}
+
+pub fn part_two(input: &str) -> usize {
+    let mut input = parse_input(input);
+    input.push(0);
+    input.sort_unstable();
+    input.push(input.last().unwrap() + 3);
+
+    let n = input.len();
+    let mut dp = vec![0; n];
+    dp[0] = 1;
+    for i in 1..n {
+        for j in (0..i).rev() {
+            if input[i] - input[j] <= 3 {
+                dp[i] += dp[j];
+            } else {
+                break;
+            }
+        }
+    }
+    dp[n - 1]
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::read_example;
+
+    #[test]
+    fn example() {
+        let input = read_example(10);
+        assert_eq!(part_one(&input), 220);
+        assert_eq!(part_two(&input), 19208);
+    }
+}

src/lib.rs

@@ -9,6 +9,7 @@ pub mod day06;
 pub mod day07;
 pub mod day08;
 pub mod day09;
+pub mod day10;
 
 pub fn read_as_string(day: u8, filename: &str) -> String {
     let filename = format!("inputs/{:02}-{}.txt", day, filename);

src/main.rs

@@ -25,6 +25,7 @@ fn main() {
         puzzle!(day07, "Handy Haversacks"),
         puzzle!(day08, "Handheld Halting"),
         puzzle!(day09, "Encoding Error"),
+        puzzle!(day10, "Adapter Array"),
     ];
 
     let filename = match env::args().find(|a| a == "--example") {