2016 day21 part2

3 files changed, 88 insertions, 44 deletions

diff --git a/src/2016/day21/aoc.cpp b/src/2016/day21/aoc.cpp
index 8c72582..fc83bb4 100644
--- a/src/2016/day21/aoc.cpp
+++ b/src/2016/day21/aoc.cpp
@@ -1,4 +1,5 @@
 #include "aoc.h"
+#include <stack>
 
 namespace aoc2016 {
 
@@ -41,14 +42,32 @@ static void rotate(char cs[8], int left, int right) {
   }
 }
 
+static void undo_rotate(char cs[8], int left, int right) { rotate(cs, right, left); }
+
 // rotate based on position of letter X
 // determine the index of letter X
 // rotate the string to the right one time
 // plus a number of times equal to that index
 // plus one additional time if the index was at least 4
-static void rotate_char(char cs[8], int x, int) {
+static void rotate_char(char cs[8], int x, int y) {
   int i = index(cs, x);
-  rotate(cs, 0, i >= 4 ? 2 + i : 1 + i);
+  int s = i >= 4 ? 2 + i : 1 + i;
+  rotate(cs, 0, s);
+}
+
+static void undo_rotate_char(char cs[8], int x, int y) {
+  char xs[8] = {0};
+  int left = 8;
+  for (int i = 0; i < 8; i++) {
+    memcpy(xs, cs, 8);
+    rotate(xs, i, 0);
+    rotate_char(xs, x, y);
+    if (memcmp(xs, cs, 8) == 0) {
+      left = i;
+      break;
+    }
+  }
+  rotate(cs, left, 0);
 }
 
 // reverse positions X through Y
@@ -77,6 +96,8 @@ static void move(char cs[8], int x, int y) {
   cs[y] = c;
 }
 
+static void undo_move(char cs[8], int x, int y) { move(cs, y, x); }
+
 typedef void (*parse)(const char*, int ds[2]);
 static void parse_swap(const char* p, int ds[2]) {
   ds[0] = *(p + 14) - '0';
@@ -112,59 +133,80 @@ static void parse_move(const char* p, int ds[2]) {
   ds[1] = *(p + 28) - '0';
 }
 
-static void print(char* cs) {
-  for (int i = 0; i < 8; i++) {
-    auto c = cs[i];
-    printf("%c", c);
+//static void print(char* cs) {
+//  for (int i = 0; i < 8; i++) {
+//    auto c = cs[i];
+//    printf("%c", c);
+//  }
+//  printf("\n");
+//}
+
+int action(const char* p) {
+  int i = 6;
+  if (*p == 's' && *(p + 5) == 'p') {
+    i = 0;
+  }
+  if (*p == 's' && *(p + 5) == 'l') {
+    i = 1;
   }
-  printf("\n");
+  if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'r') {
+    i = 2;
+  }
+  if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'l') {
+    i = 2;
+  }
+  if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'b') {
+    i = 3;
+  }
+  if (*p == 'r' && *(p + 1) == 'e') {
+    i = 4;
+  }
+  if (*p == 'm') {
+    i = 5;
+  }
+  return i;
 }
 
-std::pair<int64_t, int64_t> day21(line_view file) {
+void day21(line_view file, char cs[8], char xs[8]) {
   struct {
     parse pf;
     scramble sf;
-  } fs[] = {{parse_swap, swap},       {parse_swap_char, swap_char},
-            {parse_rotate, rotate},   {parse_rotate_char, rotate_char},
-            {parse_reverse, reverse}, {parse_move, move}};
+    scramble uf;
+  } fs[] = {{parse_swap, swap, swap},
+            {parse_swap_char, swap_char, swap_char},
+            {parse_rotate, rotate, undo_rotate},
+            {parse_rotate_char, rotate_char, undo_rotate_char},
+            {parse_reverse, reverse, reverse},
+            {parse_move, move, undo_move}};
+
+  std::vector<line_view> vs;
+  // char cs[8] = {'g', 'd', 'f', 'c', 'a', 'b', 'e', 'h'};
 
-  char cs[8] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'};
   per_line(
       file,
-      [fs](line_view lv, char cs[8]) {
+      [fs](line_view lv, char cs[8], std::vector<line_view>& vs) {
+        vs.emplace_back(lv);
         const char* p = lv.line;
         int ds[2] = {0, 0};
-        int i = 6;
-        if (*p == 's' && *(p + 5) == 'p') {
-          i = 0;
-        }
-        if (*p == 's' && *(p + 5) == 'l') {
-          i = 1;
-        }
-        if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'r') {
-          i = 2;
-        }
-        if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'l') {
-          i = 2;
-        }
-        if (*p == 'r' && *(p + 1) == 'o' && *(p + 7) == 'b') {
-          i = 3;
-        }
-        if (*p == 'r' && *(p + 1) == 'e') {
-          i = 4;
-        }
-        if (*p == 'm') {
-          i = 5;
-        }
+        int i = action(p);
         fs[i].pf(p, ds);
         fs[i].sf(cs, ds[0], ds[1]);
-        print(cs);
+        // print(cs);
         return true;
       },
-      cs);
-
-  print(cs);
-  return {0, 0};
+      cs, vs);
+
+  // char xs[8] = {'b', 'd', 'f', 'h', 'g', 'e', 'c', 'a'};
+  // print(xs);
+  for (size_t i = 0; i < vs.size(); i++) {
+    size_t ii = vs.size() - i - 1;
+    const char* p = vs[ii].line;
+    int ds[2] = {0, 0};
+    int x = action(p);
+    fs[x].pf(p, ds);
+    fs[x].uf(xs, ds[0], ds[1]);
+    // print(xs);
+  }
 }
 
 } // namespace aoc2016
diff --git a/src/2016/day21/aoc.h b/src/2016/day21/aoc.h
index 008e844..65999b9 100644
--- a/src/2016/day21/aoc.h
+++ b/src/2016/day21/aoc.h
@@ -3,5 +3,5 @@
 #include <vector>
 
 namespace aoc2016 {
-std::pair<int64_t, int64_t> day21(line_view);
+void day21(line_view, char cs[8], char xs[8]);
 }
diff --git a/test/test_2016.cpp b/test/test_2016.cpp
index d2dec77..cc3fcfd 100644
--- a/test/test_2016.cpp
+++ b/test/test_2016.cpp
@@ -188,9 +188,11 @@ TEST_CASE("Firewall Rules", "[2016]") {
 
 TEST_CASE("", "[2016]") {
   line_view lv = load_file("../src/2016/day21/input");
-  auto p = aoc2016::day21(lv);
-  REQUIRE(0 == p.first);
-  REQUIRE(0 == p.second);
+  char cs[8] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'};
+  char xs[8] = {'f', 'b', 'g', 'd', 'c', 'e', 'a', 'h'};
+  aoc2016::day21(lv,cs, xs);
+  REQUIRE(memcmp(cs, "bdfhgeca", 8) == 0);
+  REQUIRE(memcmp(xs, "gdfcabeh", 8) == 0);
 }