From 3d60859079862cd59472fc1fd47195c5722b8990 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Thu, 12 Dec 2019 08:15:01 +0100
Subject: [PATCH] Implement day 12 part 1.

---
 2019/inputs/12.txt |  4 +++
 2019/src/day12.cpp | 67 +++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 2019/inputs/12.txt

diff --git a/2019/inputs/12.txt b/2019/inputs/12.txt
new file mode 100644
index 0000000..317dac1
--- /dev/null
+++ b/2019/inputs/12.txt
@@ -0,0 +1,4 @@
+<x=-5, y=6, z=-11>
+<x=-8, y=-4, z=-2>
+<x=1, y=16, z=4>
+<x=11, y=11, z=-4>
diff --git a/2019/src/day12.cpp b/2019/src/day12.cpp
index 16cb2a8..9ab3a1a 100644
--- a/2019/src/day12.cpp
+++ b/2019/src/day12.cpp
@@ -1,8 +1,73 @@
 #include <iostream>
+#include <vector>
+#include <regex>
 #include "days.hpp"
+#include "point.hpp"
+
+namespace {
+    typedef aoc2019::Point<int, 3> point_t;
+    using aoc2019::from_chars;
+
+    std::vector<point_t> read_moons(std::istream &input) {
+        std::vector<point_t> moons;
+
+        std::regex regex(R"(^<x=(-?\d+), y=(-?\d+), z=(-?\d+)>$)");
+        std::smatch results;
+
+        for (std::string buffer; std::getline(input, buffer);) {
+            if (!std::regex_match(buffer, results, regex)) {
+                throw std::domain_error(buffer);
+            }
+
+            point_t moon;
+            for (int i = 0; i < 3; ++i) from_chars(results[i + 1].str(), moon[i]);
+
+            moons.emplace_back(moon);
+        }
+
+        return moons;
+    }
+
+    void update_velocity(const point_t &a, point_t &va, const point_t &b, point_t &vb) {
+        for (int i = 0; i < a.size(); ++i) {
+            if (a[i] < b[i]) {
+                va[i]++;
+                vb[i]--;
+            } else if (a[i] > b[i]) {
+                va[i]--;
+                vb[i]++;
+            }
+        }
+    }
+
+    void update_velocities(const std::vector<point_t> &positions, std::vector<point_t> &velocities) {
+        for (int i = 0; i < positions.size(); ++i) {
+            for (int j = i + 1; j < positions.size(); ++j) {
+                update_velocity(positions[i], velocities[i], positions[j], velocities[j]);
+            }
+        }
+    }
+}
 
 void aoc2019::day12_part1(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    auto moons = read_moons(input);
+    std::vector<point_t> velocities(moons.size());
+
+    for (int i = 0; i < 1000; ++i) {
+        update_velocities(moons, velocities);
+
+        for (int j = 0; j < moons.size(); ++j) {
+            moons[j] += velocities[j];
+        }
+    }
+
+    int energy = 0;
+
+    for (int i = 0; i < moons.size(); ++i) {
+        energy += moons[i].l1() * velocities[i].l1();
+    }
+
+	output << energy << std::endl;
 }
 
 void aoc2019::day12_part2(std::istream &input, std::ostream &output) {