this post was submitted on 02 Dec 2025
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Advent Of Code

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An unofficial home for the advent of code community on programming.dev! Other challenges are also welcome!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

Everybody Codes is another collection of programming puzzles with seasonal events.

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๐Ÿง‘ - 2025 DAY 2 SOLUTIONS - ๐Ÿง‘ (programming.dev)
submitted 2 weeks ago by CameronDev@programming.dev to c/advent_of_code@programming.dev
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Day 2: Gift Shop

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[โ€“] h4x0r@lemmy.dbzer0.com 4 points 2 weeks ago* (last edited 2 weeks ago) (3 children)

c

#include "aoc.h"
#include <stdio.h>
#include <string.h>

constexpr usize LINE_BUFSZ = (1 << 9);
constexpr usize PID_BUFSZ = (1 << 4);

static void
solve(strl re) {
  FILE* input = fopen("input", "r");
  c8 line[LINE_BUFSZ] = {};
  fgets(line, sizeof(line), input);
  line[strcspn(line, "\n")] = 0;
  usize total = 0;
  strc tok = strtok(line, ",");
  while (tok) {
    Point rng = {};
    sscanf(tok, "%zu-%zu", &rng.x, &rng.y);
    for (usize i = rng.x; i <= rng.y; i++) {
      c8 pid[PID_BUFSZ] = {};
      snprintf(pid, sizeof(pid), "%zu", i);
      is_regex_match(pid, re) ? total += i : 0;
    }
    tok = strtok(nullptr, ",");
  }
  fclose(input);
  printf("%zu\n", total);
}

i32
main(void) {
  solve("^(.+)\\1$");
  solve("^(.+)\\1+$");
}
[โ€“] h4x0r@lemmy.dbzer0.com 3 points 2 weeks ago

One last time with threads.

p1 isolated: 12ms

p2 isolated: 13ms

combined run: 25ms

typedef struct job_s {
  Mode mode;
  Point rng;
  usize total;
} Job;

static void*
worker(void* a) {
  Job* job = a;
  (job->mode == MODE_ONE) ? one(job->rng, &job->total)
                          : two(job->rng, &job->total);
  return nullptr;
}

static void
solve(Mode mode) {
  FILE* input = fopen("input", "r");
  c8 line[LINE_BUFSZ] = {};
  fgets(line, sizeof(line), input);
  line[strcspn(line, "\n")] = 0;
  fclose(input);
  usize nrng = 1;
  for (strc s = line; *s; s++) {
    if (*s == ',') {
      nrng++;
    }
  }
  Job* jobs = calloc(nrng, sizeof(*jobs));
  pthread_t* threads = calloc(nrng, sizeof(*threads));
  usize idx = 0;
  strc tok = strtok(line, ",");
  while (tok) {
    sscanf(tok, "%zu-%zu", &jobs[idx].rng.x, &jobs[idx].rng.y);
    jobs[idx].mode = mode;
    tok = strtok(nullptr, ",");
    idx++;
  }
  for (usize i = 0; i < nrng; i++) {
    pthread_create(&threads[i], nullptr, worker, &jobs[i]);
  }
  usize total = 0;
  for (usize i = 0; i < nrng; i++) {
    pthread_join(threads[i], nullptr);
    total += jobs[i].total;
  }
  free(threads);
  free(jobs);
  printf("%zu\n", total);
}

i32
main(void) {
  solve(MODE_ONE);
  solve(MODE_TWO);
}
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