1 files changed, 84 insertions, 1 deletions
diff --git a/src/2017/day16/aoc.cpp b/src/2017/day16/aoc.cpp
index 6b163a4..b1f3ae0 100644
--- a/src/2017/day16/aoc.cpp
+++ b/src/2017/day16/aoc.cpp
@@ -2,5 +2,88 @@
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day16(line_view) { return {0, 0}; }
+static int pos(char cs[16], char c) {
+  for (int i = 0; i < 16; i++) {
+    if (cs[i] == c)
+      return i;
+  }
+  return 16;
+}
+
+static void spin(char cs[16], int x) {
+  x %= 16;
+  char ts[16] = {0};
+  memcpy(ts + x, cs, 16 - x);
+  memcpy(ts, cs + 16 - x, x);
+  memcpy(cs, ts, 16);
+}
+
+static void exchange(char cs[16], int x, int y) { std::swap(cs[x], cs[y]); }
+static void partner(char cs[16], char c1, char c2) { exchange(cs, pos(cs, c1), pos(cs, c2)); }
+static void get_number(const char** pp, int* d) {
+  const char* p = *pp;
+  while (*p >= '0' && *p <= '9') {
+    *d = *d * 10 + *p - '0';
+    p++;
+  }
+  *pp = p;
+}
+
+static void print(char cs[16]) {
+  for (int i = 0; i < 16; i++) {
+    printf("%c", cs[i]);
+  }
+  printf("\n");
+}
+
+static void dance(char cs[16], line_view file) {
+  const char* p0 = file.line;
+  const char* p1 = p0;
+
+  while (p1 < file.line + file.length) {
+    if (*p1 == ',' || *p1 == '\n') {
+      switch (*p0) {
+      case 's': {
+        int d = 0;
+        p0 += 1;
+        get_number(&p0, &d);
+        spin(cs, d);
+        break;
+      }
+      case 'x': {
+        int ds[2] = {0, 0};
+        p0 += 1;
+        get_number(&p0, &ds[0]);
+        p0 += 1;
+        get_number(&p0, &ds[1]);
+        exchange(cs, ds[0], ds[1]);
+        break;
+      }
+      case 'p':
+        partner(cs, *(p0 + 1), *(p0 + 3));
+        break;
+      default:
+        break;
+      }
+      p0 = p1 + 1;
+    }
+    p1++;
+  }
+}
+
+std::pair<int64_t, int64_t> day16(line_view file) {
+  const char* s = "abcdefghijklmnop";
+  char cs[16] = {0};
+
+  for (int i = 0; i < 16; i++) {
+    cs[i] = *(s + i);
+  }
+  // size_t billion = 1000000000;
+  size_t billion = 5;
+  while (billion-- > 0) {
+    dance(cs, file);
+    print(cs);
+  }
+  return {0, 0};
+}
 } // namespace aoc2017