1 files changed, 33 insertions, 24 deletions

diff --git a/src/2017/day10/aoc.cpp b/src/2017/day10/aoc.cpp
index 1e8461e..8b652b1 100644
--- a/src/2017/day10/aoc.cpp
+++ b/src/2017/day10/aoc.cpp
@@ -20,14 +20,14 @@ knot* make_knot(int n) {
   return k;
 }
 
-static void print(knot* k) {
-  knot* n = k;
-  do {
-    printf("%d ", n->val);
-    n = n->next;
-  } while (n != k);
-  printf("\n");
-}
+// static void print(knot* k) {
+//   knot* n = k;
+//   do {
+//     printf("%d ", n->val);
+//     n = n->next;
+//   } while (n != k);
+//   printf("\n");
+// }
 
 void forward(knot** k, int n) {
   knot* x = *k;
@@ -37,8 +37,29 @@ void forward(knot** k, int n) {
   *k = x;
 }
 
-// static void reverse(knot* head, knot* tail) {
-// }
+static void reverse(knot* left, knot* right, int d) {
+  while (d-- > 0) {
+    std::swap(left->val, right->val);
+    left = left->next;
+    right = right->prev;
+  }
+}
+
+static void reverse(knot* head, int d) {
+  knot* tail = head;
+  int n = d;
+  while (--n > 0) {
+    tail = tail->next;
+  }
+  reverse(head, tail, d / 2);
+}
+
+static void reverse_skip(knot** current, int d) {
+  static int skip = 0;
+  reverse(*current, d);
+  forward(current, d + skip);
+  skip += 1;
+}
 
 static int get_number(const char** pp) {
   int d{0};
@@ -51,30 +72,18 @@ static int get_number(const char** pp) {
   return d;
 }
 
-static void reverse(knot* head, int d) {}
-
-static void reverse_skip(knot** current, int d) {
-  static int skip = 0;
-
-  reverse(*current, d);
-  forward(current, d + skip);
-  skip += 1;
-}
-
 std::pair<int64_t, int64_t> day10(line_view file) {
+  // knot* k = make_knot(5); // demo
   knot* k = make_knot(256);
 
   const char* p = file.line;
   knot* current = k;
-  print(current);
   while (p < file.line + file.length) {
     int d = get_number(&p);
-    // printf("%d\n", d);
     reverse_skip(&current, d);
     p++;
   }
 
-  print(current);
-  return {0, 0};
+  return {k->val * k->next->val, 0};
 }
 } // namespace aoc2017