From 57d678de5caf762a0066478db305af7f9c85c58f Mon Sep 17 00:00:00 2001
From: Philippe Zwietering <philippe.zwietering@gmail.com>
Date: Fri, 13 Oct 2023 14:27:00 +0200
Subject: [PATCH] Day 4 2015 advent of code

---
 advent_of_code/2015/4/Cargo.toml  |  9 ++++++
 advent_of_code/2015/4/src/main.rs | 47 +++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 advent_of_code/2015/4/Cargo.toml
 create mode 100644 advent_of_code/2015/4/src/main.rs

diff --git a/advent_of_code/2015/4/Cargo.toml b/advent_of_code/2015/4/Cargo.toml
new file mode 100644
index 0000000..04f29e4
--- /dev/null
+++ b/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"
diff --git a/advent_of_code/2015/4/src/main.rs b/advent_of_code/2015/4/src/main.rs
new file mode 100644
index 0000000..c630508
--- /dev/null
+++ b/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);
+}