1 files changed, 66 insertions, 1 deletions
diff --git a/src/2017/day20/aoc.h b/src/2017/day20/aoc.h
index 973f018..de904f8 100644
--- a/src/2017/day20/aoc.h
+++ b/src/2017/day20/aoc.h
@@ -3,5 +3,70 @@
 #include <vector>
 
 namespace aoc2017 {
+
+struct particle {
+  int64_t p[3] = {0};
+  int64_t v[3] = {0};
+  int64_t a[3] = {0};
+
+  int id;
+
+  int64_t mdistance() const noexcept { return std::abs(p[0]) + std::abs(p[1]) + std::abs(p[2]); }
+  friend bool operator<(particle p1, particle p2) { return p1.mdistance() < p2.mdistance(); }
+  friend bool operator==(particle p1, particle p2) {
+    return p1.p[0] == p2.p[0] && p1.p[1] == p2.p[1] && p1.p[2] == p2.p[2];
+  }
+
+  // Increase the X velocity by the X acceleration.
+  // Increase the Y velocity by the Y acceleration.
+  // Increase the Z velocity by the Z acceleration.
+  // Increase the X position by the X velocity.
+  // Increase the Y position by the Y velocity.
+  // Increase the Z position by the Z velocity.
+  void tick() {
+    for (int i = 0; i < 3; i++) {
+      v[i] += a[i];
+      p[i] += v[i];
+    }
+  }
+
+  void get_number(const char** pp, int64_t* d) {
+    const char* p = *pp;
+    int sign = 1;
+    if (*p == '-') {
+      sign = -1;
+      p += 1;
+    }
+    while (*p >= '0' && *p <= '9') {
+      *d = *d * 10 + *p - '0';
+      p++;
+    }
+
+    *d *= sign;
+    *pp = p;
+  }
+
+  void print() const noexcept {
+    const int64_t* d[] = {p, v, a};
+    printf("%d: ", id);
+    for (int i = 0; i < 3; i++) {
+      printf("%ld %ld %ld ", *d[i], *(d[i] + 1), *(d[i] + 2));
+    }
+    printf("\n");
+  }
+
+  particle(int x, line_view lv) : id(x) {
+    int64_t* ds[9] = {p, p + 1, p + 2, v, v + 1, v + 2, a, a + 1, a + 2};
+    int i{0};
+    const char* p = lv.line;
+    while (p < lv.line + lv.length) {
+      if (*p == '-' || (*p >= '0' && *p <= '9')) {
+        get_number(&p, ds[i++]);
+      }
+      p++;
+    }
+  }
+};
+
 std::pair<int64_t, int64_t> day20(line_view);
-}
+} // namespace aoc2017