From 0c2ac4d5f0be24026f97448ca8fab655e9901070 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Wed, 12 Jan 2022 14:28:00 +0000
Subject: [PATCH] Add 2020 puzzle 1

---
 2017/puzzle-20-01.cc | 50 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 2017/puzzle-20-01.cc

diff --git a/2017/puzzle-20-01.cc b/2017/puzzle-20-01.cc
new file mode 100644
index 0000000..d346a6a
--- /dev/null
+++ b/2017/puzzle-20-01.cc
@@ -0,0 +1,50 @@
+#include <iostream>
+#include <limits>
+#include <regex>
+#include <string>
+
+auto manhatten_distance(long x, long y, long z) { return std::abs(x) + std::abs(y) + std::abs(z); }
+
+auto main() -> int
+{
+  static std::regex re{"p=<(-?\\d+),(-?\\d+),(-?\\d+)>, v=<(-?\\d+),(-?\\d+),(-?\\d+)>, "
+                       "a=<(-?\\d+),(-?\\d+),(-?\\d+)>"};
+
+  unsigned closest{0};
+  unsigned dist_min{std::numeric_limits<unsigned>::max()};
+  unsigned ddist_min{std::numeric_limits<unsigned>::max()};
+  unsigned d2dist_min{std::numeric_limits<unsigned>::max()};
+  std::string line;
+  unsigned i{0};
+
+  while (std::getline(std::cin, line) && !line.empty()) {
+    std::smatch m;
+    if (!std::regex_search(line, m, re)) {
+      std::cerr << "Unable to interpret: " << line << '\n';
+    }
+    auto x{std::stol(m.str(1))};
+    auto y{std::stol(m.str(2))};
+    auto z{std::stol(m.str(3))};
+    auto dx{std::stol(m.str(4))};
+    auto dy{std::stol(m.str(5))};
+    auto dz{std::stol(m.str(6))};
+    auto d2x{std::stol(m.str(7))};
+    auto d2y{std::stol(m.str(8))};
+    auto d2z{std::stol(m.str(9))};
+
+    auto dist{manhatten_distance(x, y, z)};
+    auto ddist{manhatten_distance(dx, dy, dz)};
+    auto d2dist{manhatten_distance(d2x, d2y, d2z)};
+    if (d2dist < d2dist_min || (d2dist == d2dist_min && ddist < ddist_min) ||
+        (d2dist == d2dist_min && ddist == ddist_min && dist < dist_min)) {
+      d2dist_min = d2dist;
+      ddist_min = ddist;
+      dist_min = dist;
+      closest = i;
+    }
+    ++i;
+  }
+
+  std::cout << "Closest: " << closest << '\n';
+  return 0;
+}