Initial commit

2020/puzzle-23-01.cc

@@ -0,0 +1,52 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+struct Cups {
+  Cups(std::string const &s) : s_(s) {
+    std::cout << "Initial state: " << s_ << "\n";
+  }
+
+  void play(unsigned moves) {
+    // We assume the current value is always at index 0.
+    // So the values to remove are in offsets [1, 4).
+    while (moves-- > 0) {
+      char current = s_[0];
+      char d = s_[0] == '1' ? '9' : s_[0] - 1;
+      std::string::size_type dest = std::string::npos;
+      while (dest == std::string::npos) {
+        dest = s_.find(d, 4);
+        d = d == '1' ? '9' : d - 1;
+      }
+
+      s_ = s_.substr(4, dest - 3) + s_.substr(1, 3) + s_.substr(dest + 1) +
+           s_[0];
+      std::cout << moves << ": " << s_ << "\n";
+    }
+  }
+
+  std::string result() const {
+    auto split = s_.find('1');
+    return s_.substr(split + 1) + s_.substr(0, split);
+  }
+
+private:
+  std::string s_;
+};
+
+int main(void) {
+  std::string line;
+  std::getline(std::cin, line);
+  Cups cups(line);
+  cups.play(100);
+  std::cout << "Result: " << cups.result() << "\n";
+  return 0;
+}