Add 2017 day 17 puzzles.

2017/puzzle-17-02.cc

@@ -0,0 +1,32 @@
+#include <iostream>
+#include <string>
+#include <vector>
+
+using UIntVector = std::vector<unsigned>;
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read line.\n";
+    return 1;
+  }
+
+  auto step{std::stoul(line)};
+
+  unsigned pos{0};
+  unsigned after_zero{0};
+  for (unsigned i{1}; i < 50'000'001; ++i) {
+    /* Currently we have at position pos of a circular list of length i.
+     * We want to move `step` steps round the circular list.
+     */
+    pos = (pos + step) % i;
+    if (pos == 0) {
+      after_zero = i;
+    }
+    /* Current position is moved on one.  */
+    ++pos;
+  }
+  std::cout << "Result " << after_zero << '\n';
+  return 0;
+}