1 files changed, 31 insertions, 0 deletions
diff --git a/src/bin/day4.rs b/src/bin/day4.rs
new file mode 100644
index 0000000..c6963bb
--- /dev/null
+++ b/src/bin/day4.rs
@@ -0,0 +1,31 @@
+fn main() {
+    let input = "ckczppom";
+    println!("4a: {}", find_hash_count(input, "00000"));
+    println!("4b: {}", find_hash_count(input, "000000"));
+}
+
+fn find_hash_count(input: &str, start: &str) -> u32 {
+    let mut i = 0;
+
+    loop {
+        let text = input.to_string() + &i.to_string();
+        let digest = format!("{:?}", md5::compute(&text));
+
+        if digest.starts_with(start) {
+            return i;
+        }
+
+        i += 1;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        assert_eq!(find_hash_count("abcdef", "00000"), 609043);
+        assert_eq!(find_hash_count("pqrstuv", "00000"), 1048970);
+    }
+}