Day 25

day25/main.swift

@@ -0,0 +1,35 @@
+import Foundation
+
+let input = loadData(day: 25).lines().compactMap(Int.init)
+
+func loop(subject: Int, times: Int) -> Int {
+    var value = 1
+    for _ in 0..<times {
+        value = (value * subject) % 20201227
+    }
+    return value
+}
+
+func findLoopSize(subject: Int, expected: Int) -> Int {
+    var value = 1
+    for i in 0...Int.max {
+        if value == expected {
+            return i
+        }
+
+        value = (value * subject) % 20201227
+    }
+    return -1
+}
+
+let sizes = input.map { findLoopSize(subject: 7, expected: $0) }
+print(sizes)
+
+let (pub1, pub2) = (input[0], input[1])
+let (loop1, loop2) = (sizes[0], sizes[1])
+
+let secret1 = loop(subject: pub2, times: loop1)
+let secret2 = loop(subject: pub1, times: loop2)
+
+print(secret1, secret2)
+