Day 2: Red-Nosed Reports

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FAQ

  • sjmulder@lemmy.sdf.org
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    10 hours ago

    C

    First went through the input in one pass, number by number, but unfortunately that wouldn’t fly for part 2.

    Code
    #include "common.h"
    
    static int
    issafe(int *lvs, int n, int skip)
    {
    	int safe=1, asc=0,prev=0, ns=0,i;
    
    	for (i=0; safe && i<n; i++) {
    		if (i == skip)
    			{ ns = 1; continue; }
    		if (i-ns > 0)
    			safe = safe && lvs[i] != prev &&
    			    lvs[i] > prev-4 && lvs[i] < prev+4;
    		if (i-ns == 1)
    			asc = lvs[i] > prev;
    		if (i-ns > 1)
    			safe = safe && (lvs[i] > prev) == asc;
    
    		prev = lvs[i];
    	}
    
    	return safe;
    }
    
    int
    main(int argc, const char **argv)
    {
    	char buf[64], *rest, *tok;
    	int p1=0,p2=0, lvs[16],n=0, i;
    
    	if (argc > 1)
    		DISCARD(freopen(argv[1], "r", stdin));
    
    	while ((rest = fgets(buf, sizeof(buf), stdin))) {
    		for (n=0; (tok = strsep(&rest, " ")); n++) {
    			assert(n < (int)LEN(lvs));
    			lvs[n] = (int)strtol(tok, NULL, 10);
    		}
    
    		for (i=-1; i<n; i++)
    			if (issafe(lvs, n, i))
    				{ p1 += i == -1; p2++; break; }
    	}
    
    	printf("02: %d %d\n", p1, p2);
    }
    

    https://github.com/sjmulder/aoc/blob/master/2024/c/day02.c