1 files changed, 91 insertions, 0 deletions
diff --git a/src/2015/day11/aoc.cpp b/src/2015/day11/aoc.cpp
new file mode 100644
index 0000000..3489c53
--- /dev/null
+++ b/src/2015/day11/aoc.cpp
@@ -0,0 +1,91 @@
+#include "aoc.h"
+
+namespace aoc2015 {
+
+bool is_valid_rule1(int* is) {
+  auto is_valid = [](int* p) -> bool { return (*p + 1 == *(p + 1)) && (*p + 2 == *(p + 2)); };
+  for (int i = 0; i < 6; i++) {
+    if (is_valid(is + i)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool is_valid_rule3(int* is) {
+  int* p1 = nullptr;
+  int* p2 = nullptr;
+  int* p3 = is + 7;
+  while (is < p3) {
+    if (*is == *(is + 1)) {
+      if (p1 == nullptr) {
+        p1 = is;
+      } else {
+        p2 = is;
+      }
+      is += 2;
+    } else {
+      is += 1;
+    }
+  }
+  return p1 != nullptr && p2 != nullptr && *p1 != *p2;
+}
+
+// int* 0..25
+void next(int* is, int* invalids, int n) {
+  // increatment
+  for (int x = 7; x >= 0; x--) {
+    if (is[x] == 'z' - 'a') {
+      is[x] = 0;
+    } else {
+      is[x] += 1;
+      break;
+    }
+  }
+
+  auto is_invalid = [invalids, n](int x) -> bool {
+    for (int j = 0; j < n; j++) {
+      if (x == invalids[j]) {
+        return true;
+      }
+    }
+    return false;
+  };
+
+  for (int x = 0; x < 8; x++) {
+    if (is_invalid(is[x])) { // is[x] = 'i' 'j' 'o'
+      is[x] = is[x] == 25 ? 0 : is[x] + 1;
+      for (int k = x + 1; k < 8; k++) {
+        is[k] = 0;
+      }
+      break;
+    }
+  }
+}
+
+char* day11(const char* pass) {
+  int invalids[] = {'i' - 'a', 'o' - 'a', 'l' - 'a'};
+  int indexes[8] = {0};
+  for (int i = 0; i < 8; i++) {
+    indexes[i] = pass[i] - 'a';
+  }
+
+  bool b1 = false;
+  bool b3 = false;
+
+  do {
+    next(indexes, invalids, ARRAY_SIZE(invalids));
+    b1 = is_valid_rule1(indexes);
+    b3 = is_valid_rule3(indexes);
+  } while (!b1 || !b3);
+
+  char* password = (char*)malloc(9);
+  for (int i = 0; i < 8; i++) {
+    password[i] = 'a' + indexes[i];
+  }
+  password[8] = '\0';
+
+  return password;
+}
+
+} // namespace aoc2015