day 9

d09.cc

@@ -0,0 +1,108 @@
+#include <iostream>
+#include <vector>
+#include <unordered_set>
+
+using namespace std;
+
+enum Dir {
+    UP,
+    DOWN,
+    RIGHT,
+    LEFT
+};
+
+struct Instr {
+    enum Dir dir;
+    unsigned steps;
+};
+
+struct Pos2d {
+    int x, y;
+
+    Pos2d operator+(const Pos2d &r) const
+    {
+        return {this->x + r.x, this->y + r.y};
+    }
+    void operator+=(const Pos2d &r) { *this = *this + r; }
+
+    Pos2d operator-(const Pos2d &r) const
+    {
+        return {this->x - r.x, this->y - r.y};
+    }
+
+    bool operator==(const Pos2d &r) const
+    {
+        return this->x == r.x && this->y == r.y;
+    }
+};
+
+Pos2d dirs[] = {
+    {0, 1},
+    {0, -1},
+    {1, 0},
+    {-1, 0}
+};
+
+typedef vector<Instr> Input;
+
+template<>
+struct std::hash<Pos2d> {
+    size_t operator()(const Pos2d &r) const
+    {
+        return hash<int>{}(r.x) ^ (hash<int>{}(r.y) << 1);
+    }
+};
+
+Input parse()
+{
+    Input data;
+    for (string line; getline(cin, line);) {
+        Instr instr;
+        if (line.size() < 3 || line.at(1) != ' ') throw "parse";
+        switch (line.at(0)) {
+        case 'U': instr.dir = UP; break;
+        case 'D': instr.dir = DOWN; break;
+        case 'L': instr.dir = LEFT; break;
+        case 'R': instr.dir = RIGHT; break;
+        }
+        instr.steps = stoi(line.substr(2));
+        data.push_back(instr);
+    }
+    return data;
+}
+
+unsigned p1(const Input &input, unsigned count = 2)
+{
+    auto knot = vector<Pos2d>(count);
+    unordered_set<Pos2d> visited;
+    visited.insert(knot.back());
+    for (auto x : input) {
+        for (unsigned i = 0; i < x.steps; i++) {
+            knot.front() += dirs[x.dir];
+            for (auto el = knot.begin(); el < knot.end() - 1; el++) {
+                Pos2d dist = el[0] - el[1];
+                if (abs(dist.x) >= 2 || abs(dist.y) >= 2) {
+                    if (abs(dist.x) >= 2) dist.x = dist.x > 0 ? 1 : -1;
+                    if (abs(dist.y) >= 2) dist.y = dist.y > 0 ? 1 : -1;
+                    el[1] += dist;
+                    continue;
+                }
+                break;
+            }
+            visited.insert(knot.back());
+        }
+    }
+    return visited.size();
+}
+
+unsigned p2(const Input &input)
+{
+    return p1(input, 10);
+}
+
+int main()
+{
+    auto input = parse();
+    cout << p1(input) << endl;
+    cout << p2(input) << endl;
+}

d09_output.txt

@@ -0,0 +1,2 @@
+5930
+2443