Initial commit

2015/puzzle-11-02.cc

@@ -0,0 +1,78 @@
+#include <cassert>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <variant>
+
+bool illegal_char(char c) { return c == 'i' || c == 'l' || c == 'o'; }
+
+void pre_advance_password(std::string &s) {
+  std::string::size_type pos = 0;
+  while (pos < s.length() && !illegal_char(s[pos])) {
+    ++pos;
+  }
+  if (pos == s.length()) {
+    return;
+  }
+  ++s[pos++];
+  while (pos < s.length()) {
+    s[pos++] = 'a';
+  }
+}
+
+void advance_password(std::string &s) {
+  auto pos = s.length() - 1;
+  while (true) {
+    if (s[pos] == 'z') {
+      assert(pos != 0);
+      s[pos] = 'a';
+      pos -= 1;
+    } else {
+      ++s[pos];
+      if (illegal_char(s[pos])) {
+        ++s[pos];
+      }
+      return;
+    }
+  }
+}
+
+bool valid_password(std::string const &s) {
+  unsigned double_count = 0;
+  bool run = false;
+  char last2 = '\0';
+  char last = '\0';
+  for (auto c : s) {
+    if (c == last && last2 != c) {
+      ++double_count;
+    } else if (c == last + 1 && c == last2 + 2) {
+      run = true;
+    }
+    last2 = last;
+    last = c;
+  }
+
+  return double_count >= 2 && run;
+}
+
+std::string next_password(std::string const &s) {
+  std::string result = s;
+  pre_advance_password(result);
+  do {
+    advance_password(result);
+  } while (!valid_password(result));
+  return result;
+}
+
+int main(int argc, char **argv) {
+  for (std::string line; std::getline(std::cin, line);) {
+    std::string next = next_password(line);
+    std::string next2 = next_password(next);
+    std::cout << "Current password: " << line << "; Next password: " << next
+              << "; Subsequent password: " << next2 << "\n";
+  }
+  return 0;
+}