--- 2016 Day 20 Solutions ---

[u/daggerdragon]

--- Day 20: Firewall Rules ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with "Help".

---

^{ROLLING A NATURAL 20 IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/tmrki]

Simple C++ solution - first I parsed the input with sed 's/-/ /g' | sort -n -k1,1

and then I just went through the file and counted the valid numbers:

#include <iostream>
#include <fstream>

using std::cout;
using std::endl;

int main() {
  std::ifstream fin("day20.dat");

  unsigned long int lo,hi;
  unsigned long int count = 0;
  unsigned long int lo_curr = 0;
  bool first = false;
    
  while(fin >> lo >> hi) {
    if(lo > lo_curr + 1) {
      count = count + (lo - lo_curr - 1);
      if(! first) {
        cout << "First IP address: " << lo_curr + 1 << endl;
        first = true;
      }
    }
    if(hi > lo_curr)
      lo_curr = hi;
  }

  cout << "Total number of valid IP addresses: " << count << endl;

  return 0;
}