Add solution for 2015 Day 25

src/common/lib/Helper.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdint.h>
+
 #include <algorithm>
 #include <array>
 #include <functional>
@@ -607,6 +609,24 @@ struct Helper
     return currentRes;
   }
 
+  static uint64_t FastExponentiation(uint64_t start, uint64_t multiplication, uint64_t power, uint64_t mod)
+  {
+    while (power > 0)
+    {
+      if (power % 2 == 0)
+      {
+        multiplication = (multiplication * multiplication) % mod;
+        power /= 2;
+      }
+      else
+      {
+        start = (start * multiplication) % mod;
+        power--;
+      }
+    }
+    return start;
+  }
+
   // Input    - Puzzle input
   // Function - bool(int64_t);
   //            Given index, return whether the index should increase next