116 lines
2.8 KiB
C
116 lines
2.8 KiB
C
/* aoc-c.c: Advent2020, day 23, part 1
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <ctype.h>
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#include "list.h"
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#include "debug.h"
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/* Here we will simply use an array for the numbers (as key is the number
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* itself). All elements make a next/prev ring.
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* Note: we will ignore array[0] to avoid millions of useless "position -1"
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* calculations
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*/
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struct list_head *curcup; /* current cup */
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struct list_head *cups; /* the cups cups */
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int lastnum; /* last cup number */
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#define CUR_CUP (&*curcup)
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#define NUM(pcup) ((pcup) - cups)
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static __always_inline void step()
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{
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struct list_head *first, *last, *dest = CUR_CUP;
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int num[3] = { 0 };
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first = CUR_CUP->next;
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last = first->next->next;
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num[0] = NUM(first);
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num[1] = NUM(first->next);
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num[2] = NUM(last);
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do {
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if (NUM(--dest) <= 0)
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dest = &cups[lastnum];
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} while (NUM(dest) == num[0] || NUM(dest) == num[1] || NUM(dest) == num[2]);
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list_bulk_move(dest, first, last);
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curcup = CUR_CUP->next;
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}
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/**
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* parse - initialize cups list.
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*/
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static void parse(int last)
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{
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int count = 0, c;
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cups = malloc(sizeof(struct list_head) * (last + 1));
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if (cups) {
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for (c = getchar(); isdigit(c); c = getchar(), ++count) {
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struct list_head *next = &cups[c - '0'];
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if (!count) /* first cup */
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INIT_LIST_HEAD(curcup = next);
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else
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list_add_tail(&cups[c - '0'], CUR_CUP);
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}
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for (++count; count <= last; ++count) /* add remaining cups */
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list_add_tail(&cups[count], CUR_CUP);
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}
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}
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static long part1()
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{
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struct list_head *cur;
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int res = 0;
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list_for_each(cur, &cups[1]) {
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res = res * 10 + NUM(cur);
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}
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return res;
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}
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static long part2()
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{
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return NUM((&cups[1])->next) * NUM((&cups[1])->next->next);
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}
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static int usage(char *prg)
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{
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fprintf(stderr, "Usage: %s [-d debug_level] [-p part]\n", prg);
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return 1;
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}
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int main(ac, av)
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int ac;
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char **av;
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{
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int opt, part = 1;
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while ((opt = getopt(ac, av, "d:p:")) != -1) {
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switch (opt) {
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case 'd':
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debug_level_set(atoi(optarg));
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break;
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case 'p': /* 1 or 2 */
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part = atoi(optarg);
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if (part < 1 || part > 2)
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default:
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return usage(*av);
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}
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}
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lastnum = part == 1? 9: 1000000;
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int loops = part == 1? 100: 10000000;
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parse(lastnum);
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for (int i = 0; i < loops; ++i)
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step();
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printf("%s : res=%ld\n", *av, part == 1? part1(): part2());
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free(cups);
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exit (0);
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}
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