adventofcode2025/adventofcodeday7.c at main · pPyrius/adventofcode2025 · GitHub

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
  char *lines[2];
  int sum;
} manifold;

void process_lines(manifold *m) {
  for (int i = 0; i < strlen(m->lines[0]); i++) {
    if (m->lines[0][i] == 'S') {
      m->lines[1][i] = '|';
    } else if (m->lines[1][i] == '^') {
      if (m->lines[0][i] == '|') {
        m->sum++;
        if (i != 0)
          m->lines[1][i - 1] = '|';
        if (i != strlen(m->lines[0]) - 1)
          m->lines[1][i + 1] = '|';
      }
    } else if (m->lines[0][i] == '|') {
      if (m->lines[1][i] == '.') {
        m->lines[1][i] = '|';
      }
    }
  }
}

void shift_lines(manifold *m) {
  memcpy(m->lines[0], m->lines[1], strlen(m->lines[1]) + 1);
  memset(m->lines[1], '\0', strlen(m->lines[0]) + 1);
}

void resolve_manifold(FILE *file, manifold *m) {
  size_t len = 500;
  if (getline(&m->lines[0], &len, file) == -1) {
    printf("Error reading file\n");
    return;
  }
  int nread;
  while ((nread = getline(&m->lines[1], &len, file)) != -1) {
    process_lines(m);
    shift_lines(m);
  }
  printf("Sum: %d\n", m->sum);
}

int main(void) {
  manifold *m = malloc(sizeof(manifold));
  m->sum = 0;
  FILE *file = fopen("input", "r");
  if (file == NULL) {
    printf("Error opening file\n");
    return 1;
  }
  resolve_manifold(file, m);

  fclose(file);
}