C

Merry Christmas everyone!

#include "common.h"

int
main(int argc, char **argv)
{
	static char buf[7];
	static short h[500][5];	/* heights */
	static short iskey[500];
	int p1=0, nh=0, i,j,k;

	if (argc > 1)
		DISCARD(freopen(argv[1], "r", stdin));
	
	for (nh=0; !feof(stdin) && !ferror(stdin); nh++) {
		assert(nh < (int)LEN(h));

		for (i=0; i<7; i++) {
			fgets(buf, 7, stdin);
			if (i==0)
				iskey[nh] = buf[0] == '#';
			for (j=0; j<5; j++)
				h[nh][j] += buf[j] == '#';
		}

		/* skip empty line */
		fgets(buf, 7, stdin);
	}

	for (i=0; i<nh; i++)
	for (j=0; j<nh; j++)
		if (iskey[i] && !iskey[j]) {
			for (k=0; k<5 && h[i][k] + h[j][k] <= 7; k++) ;
			p1 += k == 5;
		}

	printf("25: %d\n", p1);
	return 0;
}

https://codeberg.org/sjmulder/aoc/src/branch/master/2024/c/day25.c

Made the 1 second challenge with most of it to spare! 😎

$ time bmake bench                                                                                                      
day01  0:00.00  1912 Kb  0+88 faults                                                                                            
day02  0:00.00  1992 Kb  0+91 faults 
day03  0:00.00  1920 Kb  0+93 faults
day04  0:00.00  1912 Kb  0+90 faults 
day05  0:00.00  2156 Kb  0+91 faults
day06  0:00.03  1972 Kb  0+100 faults
day07  0:00.06  1892 Kb  0+89 faults
day08  0:00.00  1772 Kb  0+87 faults 
day09  0:00.02  2024 Kb  0+137 faults
day10  0:00.00  1876 Kb  0+87 faults 
day11  0:00.00  6924 Kb  0+3412 faults
day12  0:00.00  1952 Kb  0+103 faults
day13  0:00.00  1908 Kb  0+88 faults
day14  0:00.05  1944 Kb  0+92 faults                                                                                            
day15  0:00.00  2040 Kb  0+89 faults
day16  0:00.03  2020 Kb  0+250 faults
day17  0:00.00  1896 Kb  0+88 faults
day18  0:00.00  1952 Kb  0+107 faults
day19  0:00.01  1904 Kb  0+91 faults
day20  0:00.01  2672 Kb  0+325 faults
day21  0:00.00  1804 Kb  0+86 faults
day22  0:00.03  2528 Kb  0+371 faults
day23  0:00.02  2064 Kb  0+152 faults
day24  0:00.00  1844 Kb  0+89 faults
day25  0:00.00  1788 Kb  0+89 faults  
                                                                
real    0m0,359s