2015: day04: part 1

aoc2015/Cargo.toml

@@ -9,3 +9,4 @@ edition = "2018"
 [dependencies]
 
 aoc = { path = "../aoc" }
+md-5 = "0.8"

aoc2015/input/day04.txt

@@ -0,0 +1 @@
+yzbqklnj

aoc2015/src/day04.rs

@@ -0,0 +1,48 @@
+use md5::{Digest, Md5};
+
+use aoc::err;
+use aoc::Result;
+
+const INPUT: &str = include_str!("../input/day04.txt");
+
+pub fn run() -> Result<()> {
+    println!("part 1: {}", part1(INPUT)?);
+
+    Ok(())
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let input = input.trim_end();
+
+    let mut hasher = Md5::new();
+
+    for i in 0.. {
+        let content = format!("{}{}", input, i);
+
+        hasher.input(content);
+        let res = format!("{:x}", hasher.result_reset());
+        if &res[..5] == "00000" {
+            return Ok(i);
+        }
+    }
+
+    Err(err!("couldn't find a suitable number"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[ignore] // takes too long!
+    fn part1_provided() {
+        assert_eq!(part1("abcdef").unwrap(), 609043);
+        assert_eq!(part1("pqrstuv").unwrap(), 1048970);
+    }
+
+    #[test]
+    #[ignore] // takes too long!
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 282749);
+    }
+}

aoc2015/src/lib.rs

@@ -1,3 +1,4 @@
 pub mod day01;
 pub mod day02;
 pub mod day03;
+pub mod day04;

aoc2015/src/main.rs

@@ -3,9 +3,10 @@ use aoc::Result;
 use aoc2015::day01;
 use aoc2015::day02;
 use aoc2015::day03;
+use aoc2015::day04;
 
 fn main() -> Result<()> {
-    let days: &[fn() -> Result<()>] = &[day01::run, day02::run, day03::run];
+    let days: &[fn() -> Result<()>] = &[day01::run, day02::run, day03::run, day04::run];
 
     aoc::run(days)
 }