1 files changed, 72 insertions, 0 deletions
diff --git a/src/2016/day4/aoc.cpp b/src/2016/day4/aoc.cpp
index 55f4247..895725d 100644
--- a/src/2016/day4/aoc.cpp
+++ b/src/2016/day4/aoc.cpp
@@ -1,5 +1,77 @@
 #include "aoc.h"
+#include <algorithm>
+#include <string.h>
+#include <vector>
 
 namespace aoc2016 {
 
+struct ccount {
+  char c;
+  int count;
+
+  bool operator<(const ccount& other) const noexcept {
+    return count > other.count ? true : (count < other.count ? false : c < other.c);
+  };
+};
+
+unsigned char shift(unsigned char c, int times) {
+  if (c == '-') {
+    return ' ';
+  }
+  times %= 26;
+  c += times;
+  if (c > 'z') {
+    c = 'a' + c - 'z' - 1;
+  }
+  return c;
 }
+
+bool is_real_room(line_view lv, int* id, char names[]) {
+  const char* p = lv.line;
+  while (!(*p >= '0' && *p <= '9')) {
+    p++;
+  }
+  const char* p0 = p;
+
+  ascii_count ac{{lv.line, p}};
+  std::vector<ccount> cc;
+  for (char i = 'a'; i <= 'z'; i++) {
+    cc.push_back({i, ac.count[int(i)]});
+  }
+  std::sort(cc.begin(), cc.end());
+
+  while (*p >= '0' && *p <= '9') {
+    *id = *id * 10 + *p - '0';
+    p++;
+  }
+  int x{0};
+  for (const char* p1 = lv.line; p1 != p0; p1++) {
+    names[x++] = shift(*p1, *id);
+  }
+  for (int i = 0; i < 5; i++) {
+    if (*(p + i + 1) != cc[i].c) {
+      return false;
+    }
+  }
+  return true;
+}
+
+std::pair<int, int> day4(line_view file) {
+  int total{0};
+  int pole_id{0};
+  per_line(file, [&total, &pole_id](line_view lv) {
+    int id{0};
+    char names[100] = {0};
+    if (is_real_room(lv, &id, names)) {
+      // printf("%d %s\n", id, names);
+      if (strstr(names, "northpole")) {
+        pole_id = id;
+      }
+      total += id;
+    }
+    return true;
+  });
+  return {total, pole_id};
+}
+
+} // namespace aoc2016