1 files changed, 40 insertions, 0 deletions
diff --git a/2017/src/bin/day_15.rs b/2017/src/bin/day_15.rs
new file mode 100644
index 0000000..29b63ad
--- /dev/null
+++ b/2017/src/bin/day_15.rs
@@ -0,0 +1,40 @@
+extern crate advent_of_code_2017;
+use advent_of_code_2017::*;
+
+fn main() {
+    let args = AdventArgs::init();
+
+    let mut a: u64 = 591;
+    let mut b: u64 = 393;
+
+    let mut matches: u64 = 0;
+
+    let comparisons = if args.part == 1 {
+        40_000_000
+    } else {
+        5_000_000
+    };
+    
+    for _ in 0..comparisons {
+        a = (a * 16807) % 2147483647;
+        b = (b * 48271) % 2147483647;
+
+        while args.part != 1 && a % 4 != 0 {
+            a = (a * 16807) % 2147483647;
+        }
+        while args.part != 1 && b % 8 != 0 {
+            b = (b * 48271) % 2147483647;
+        }
+        
+        if lower_16_match(a, b) {
+            matches += 1;
+        }
+    }
+
+    println!("There were {} matches", matches);
+}
+
+fn lower_16_match(a: u64, b: u64) -> bool {
+    let mask = 65535; //2^16-1, ie 16 ones
+    (a & mask) == (b & mask)
+}