aoc 2016, day 1

1 files changed, 122 insertions, 0 deletions

diff --git a/2016/src/day01.cpp b/2016/src/day01.cpp
new file mode 100644
index 0000000..f5d74a5
--- /dev/null
+++ b/2016/src/day01.cpp
@@ -0,0 +1,122 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+split(string_view line, string_view delimiter)
+{
+        size_t pos_start = 0;
+        size_t pos_end   = 0;
+
+        vector<string> res;
+
+        while ( (pos_end = line.find(delimiter, pos_start)) != string::npos ) {
+                auto token = line.substr(pos_start, pos_end - pos_start);
+                pos_start  = pos_end + delimiter.length();
+
+                res.emplace_back(token);
+        }
+
+        if ( pos_start != line.size() ) {
+                res.emplace_back(line.substr(pos_start));
+        }
+        return res;
+}
+
+vector<tuple<char, long>>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+        string  content{ istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
+
+        vector<tuple<char, long>> result;
+        for ( const auto& part: split(content, ", ") ) {
+                result.emplace_back(part[0], stol(part.substr(1)));
+        }
+        return result;
+}
+
+void
+part1(const vector<tuple<char, long>>& input)
+{
+        array<tuple<long, long>, 4> dirs = {
+                make_tuple(1L, 0L),
+                make_tuple(0L, 1L),
+                make_tuple(-1L, 0L),
+                make_tuple(0L, -1L)
+        };
+
+        size_t dir   = 0;
+        long   pos_x = 0;
+        long   pos_y = 0;
+
+        for ( const auto& [change, length]: input ) {
+                if ( change == 'L' ) {
+                        dir = (dir + 1) % 4;
+                }
+                else {
+                        dir = (dir + 3) % 4;
+                }
+
+                auto [delta_x, delta_y] = dirs.at(dir);
+
+                pos_x += length * delta_x;
+                pos_y += length * delta_y;
+        }
+
+        cout << abs(pos_x) + abs(pos_y) << endl;
+}
+
+void
+part2(const vector<tuple<char, long>>& input)
+{
+        array<tuple<long, long>, 4> dirs = {
+                make_tuple(1L, 0L),
+                make_tuple(0L, 1L),
+                make_tuple(-1L, 0L),
+                make_tuple(0L, -1L)
+        };
+
+        size_t dir   = 0;
+        long   pos_x = 0;
+        long   pos_y = 0;
+
+        set<tuple<long, long>> visited;
+
+        for ( auto [change, length]: input ) {
+                if ( change == 'L' ) {
+                        dir = (dir + 1) % 4;
+                }
+                else {
+                        dir = (dir + 3) % 4;
+                }
+
+                auto [delta_x, delta_y] = dirs.at(dir);
+
+                while ( length-- > 0 ) {
+                        pos_x += delta_x;
+                        pos_y += delta_y;
+
+                        if ( visited.contains({ pos_x, pos_y }) ) {
+                                cout << abs(pos_x) + abs(pos_y) << endl;
+                                return;
+                        }
+
+                        visited.emplace(pos_x, pos_y);
+                }
+        }
+}
+
+int
+main()
+{
+        auto input = read_file("data/day01.txt");
+        part1(input);
+        part2(input);
+}