Initial commit

2020/puzzle-13-02.cc

@@ -0,0 +1,55 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <climits>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <string>
+
+using Time = unsigned long;
+using IDPair = std::pair<Time, Time>;
+using IDVector = std::vector<IDPair>;
+
+int main(int argc, char **argv) {
+  std::string line;
+  std::getline(std::cin, line); // Ignore first line
+
+  std::string buses;
+  std::getline(std::cin, buses);
+  std::string::size_type pos = 0;
+  Time offset = 0;
+  IDVector ids;
+
+  while (pos < buses.size()) {
+    if (buses[pos] == ',') {
+      ++pos;
+      continue;
+    } else if (buses[pos] == 'x') {
+      ++offset;
+      ++pos;
+      continue;
+    }
+
+    std::string::size_type len = 0;
+    Time depart = std::stoul(buses.substr(pos), &len);
+    std::cout << "Bus #" << depart << " at offset " << offset << "\n";
+    ids.push_back(std::make_pair(depart, offset));
+    pos += len;
+    ++offset;
+  }
+
+  // Make assumption that all bus IDs are co-prime.
+  Time t = 0;
+  Time t_incr = 1;
+  for (auto const &bus : ids) {
+    while ((t + bus.second) % bus.first != 0) {
+      t += t_incr;
+    }
+    std::cout << "Bus #" << bus.first << " at offset " << bus.second
+              << " t = " << t << "\n";
+    t_incr *= bus.first;
+  }
+  return 0;
+}