1 files changed, 94 insertions, 0 deletions

diff --git a/2017/src/day03.cpp b/2017/src/day03.cpp
new file mode 100644
index 0000000..417cef3
--- /dev/null
+++ b/2017/src/day03.cpp
@@ -0,0 +1,94 @@
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <iostream>
+#include <map>
+
+using namespace std;
+
+namespace {
+
+void
+part1(int value)
+{
+        auto ring      = static_cast<int>(ceil((sqrt(value) - 1) / 2));
+        auto side_len  = (2 * ring) + 1;
+        auto max_value = side_len * side_len;
+
+        array<int, 4> centers = {
+                max_value - ring - (2 * ring * 0),
+                max_value - ring - (2 * ring * 1),
+                max_value - ring - (2 * ring * 2),
+                max_value - ring - (2 * ring * 3)
+        };
+
+        auto* itr = ranges::min_element(centers, {}, [value](int rhs) { return abs(value - rhs); });
+
+        auto dist_to_center = abs(value - *itr);
+
+        cout << "Part1: " << ring + dist_to_center << '\n';
+}
+
+void
+part2(int value)
+{
+        static const array<tuple<int, int>, 4> dirs{
+                make_tuple(1, 0),  // right
+                make_tuple(0, -1), // up
+                make_tuple(-1, 0), // left
+                make_tuple(0, 1),  // down
+        };
+
+        static const array<int, 3> offsets = { -1, 0, 1 };
+
+        map<tuple<int, int>, int> grid; // (x,y) => value
+
+        int x     = 0;
+        int y     = 0;
+        int steps = 1;
+
+        grid[{ x, y }] = 1;
+
+        while ( true ) {
+                for ( const auto [dx, dy]: dirs ) {
+                        for ( int _ = 0; _ != steps; ++_ ) {
+                                x += dx;
+                                y += dy;
+
+                                int sum = 0;
+                                for ( const auto off_x: offsets ) {
+                                        for ( const auto off_y: offsets ) {
+                                                if ( off_x == 0 && off_y == 0 ) {
+                                                        continue;
+                                                }
+
+                                                const auto pos = make_tuple(x + off_x, y + off_y);
+                                                if ( grid.contains(pos) ) {
+                                                        sum += grid.at(pos);
+                                                }
+                                        }
+                                }
+
+                                if ( sum > value ) {
+                                        cout << "Part2: " << sum << '\n';
+                                        return;
+                                }
+
+                                grid[{ x, y }] = sum;
+                        }
+                        if ( dx == 0 ) {
+                                ++steps;
+                        }
+                }
+        }
+}
+
+} // namespace
+
+int
+main()
+{
+        static const auto puzzle = 265149;
+        part1(puzzle);
+        part2(puzzle);
+}