Finish day 4

Cargo.lock

@@ -5,3 +5,12 @@ version = 3
 [[package]]
 name = "AoC2015"
 version = "0.1.0"
+dependencies = [
+ "md5",
+]
+
+[[package]]
+name = "md5"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "490cc448043f947bae3cbee9c203358d62dbee0db12107a74be5c30ccfd09771"

Cargo.toml

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+md5 = "0.7.0"

src/day4.rs

@@ -0,0 +1,39 @@
+use md5;
+
+pub fn run() {
+    println!("Day 4:");
+    let input = "yzbqklnj".to_string();
+
+    println!("\tPart 1: {}", part1(&input, 5));
+    println!("\tPart 2: {}", part1(&input, 6));
+}
+
+fn part1(input: &String, zeros: usize) -> usize {
+    let mut key: usize = 0;
+
+    let max_iter = 1e9 as usize;
+    loop {
+        let digest = md5::compute(format!("{}{}", input, key));
+
+        if format!("{:x},", digest).starts_with(&"0".repeat(zeros)) {
+            return key;
+        }
+
+        key += 1;
+
+        if key == max_iter {
+            return 0;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_1() {
+        assert_eq!(part1(&"abcdef".to_string(), 5), 609043);
+        assert_eq!(part1(&"pqrstuv".to_string(), 5), 1048970);
+    }
+}

src/main.rs

@@ -1,10 +1,12 @@
 mod day1;
 mod day2;
 mod day3;
+mod day4;
 
 fn main() {
     println!("Running Advent of Code 2021");
     day1::run();
     day2::run();
     day3::run();
+    day4::run();
 }