aoc24/11/main.cc

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <unordered_map>
#include "hash.h"

using namespace std;

struct Node {
  unsigned long long value;
  Node *next;
};

Node *parseList(const char *path) {
  ifstream input(path);
  string line;

  getline(input, line);
  stringstream ss;
  ss << line;
  unsigned long long a;

  // head
  ss >> a;
  Node *curr = new Node();
  curr->value = a;
  Node *head = curr;

  // rest
  while (ss >> a) {
    Node *prev = curr;
    curr = new Node();
    curr->value = a;
    prev->next = curr;
  }

  return head;
}

void blink(Node *head) {
  Node *curr = head;
  while (curr != nullptr) {
    // get next already, to skip newly appended elements
    Node *next = curr->next;

    // do blink
    string num = to_string(curr->value);
    if (curr->value == 0) {
      curr->value = 1;
    } else if (num.size() % 2 == 0) {
      string num1 = num.substr(0, num.size() / 2);
      string num2 = num.substr(num.size() / 2, num.size() / 2);

      Node *new_node = new Node();
      curr->value = stol(num1);
      curr->next = new_node;
      new_node->value = stol(num2);
      new_node->next = next;
    } else {
      curr->value = curr->value * 2024;
    }
    curr = next;
  }
}

int length(Node *head) {
  int ret = 0;
  Node *curr = head;
  while (curr != nullptr) {
    ret++;
    curr = curr->next;
  }
  return ret;
}

void printList(Node *head) {
  Node *curr = head;

  while (curr != nullptr) {
    cout << curr->value << " ";
    curr = curr->next;
  }
  cout << endl;
}

// highly inefficient
int part1(const char *path) {
  Node *head = parseList(path);
  for (int i = 0; i < 25; i++) {
    blink(head);
  }

  return length(head);
}

unordered_map<tuple<long, int>, long> memo;

unsigned long long doBlinks(unsigned long long value, int iterations) {
  if (iterations == 0) {
    return 1;
  }

  // cache hit
  if (memo.count(make_tuple(value, iterations))) {
    // return memo.at(make_tuple(value, iterations));
    return memo[make_tuple(value, iterations)];
  }

  // cache miss -> do blink
  if (value == 0) {
    long ret = doBlinks(1 , iterations - 1);
    memo[make_tuple(value, iterations)] = ret;
    return ret;
  }

  unsigned long long ret = 0;
  string num = to_string(value);
  if (num.size() % 2 == 0) {
    string num1 = num.substr(0, num.size() / 2);
    string num2 = num.substr(num.size() / 2, num.size() / 2);
    ret += doBlinks(stol(num1), iterations - 1);
    ret += doBlinks(stol(num2), iterations - 1);
    memo[make_tuple(value, iterations)] = ret;
    return ret;
  } else {
    long ret = doBlinks(value * 2024, iterations - 1);
    memo[make_tuple(value, iterations)] = ret;
    return ret;
  }
}

unsigned long long part2(const char *path) {
  Node *head = parseList(path);

  unsigned long long sum = 0;

  while (head != nullptr) {
    sum += doBlinks(head->value, 75);
    head = head->next;
  }

  return sum;
}

int main(int argc, char *argv[]) {
  cout << "example1: " << part1("example") << endl;
  cout << "input1: " << part1("input") << endl;
  cout << "example2: " << part2("example") << endl;
  cout << "input2: " << part2("input") << endl;
  return 0;;
}