Day 4 2015 advent of code

advent_of_code/2015/4/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "main"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+md5 = "0.7.0"

advent_of_code/2015/4/src/main.rs

@@ -0,0 +1,47 @@
+const INPUT: &str = "iwrupvqb";
+
+fn solve(input: &str, desired_start: &str) -> u64 {
+    let mut postfix = 1;
+    loop {
+        let digest = md5::compute(format!("{input}{postfix}"));
+        let digest = format!("{:x?}", digest);
+
+        if digest.starts_with(desired_start) {
+            return postfix;
+        }
+
+        postfix += 1;
+    }
+}
+
+fn main() {
+    println!("Hello, this is Patrick!");
+
+    let first_result = solve(INPUT, "00000");
+
+    println!(
+        "Santa needs to use a safer hashing, but his result is: {}",
+        first_result
+    );
+
+    let second_result = solve(INPUT, "000000");
+
+    println!(
+        "The extra zero costs a lot and has the answer: {}",
+        second_result
+    );
+}
+
+#[test]
+fn test_first1() {
+    let s = solve("abcdef", "00000");
+
+    assert_eq!(s, 609043);
+}
+
+#[test]
+fn test_first2() {
+    let s = solve("pqrstuv", "00000");
+
+    assert_eq!(s, 1048970);
+}