day 4 (C)
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@@ -57,3 +57,18 @@ At this point, the third board wins because it has at least one complete row or
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The score of the winning board can now be calculated. Start by finding the sum of all unmarked numbers on that board; in this case, the sum is 188. Then, multiply that sum by the number that was just called when the board won, 24, to get the final score, 188 * 24 = 4512.
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To guarantee victory against the giant squid, figure out which board will win first. What will your final score be if you choose that board?
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Your puzzle answer was 25410.
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--- Part Two ---
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On the other hand, it might be wise to try a different strategy: let the giant squid win.
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You aren't sure how many bingo boards a giant squid could play at once, so rather than waste time counting its arms, the safe thing to do is to figure out which board will win last and choose that one. That way, no matter which boards it picks, it will win for sure.
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In the above example, the second board is the last to win, which happens after 13 is eventually called and its middle column is completely marked. If you were to keep playing until this point, the second board would have a sum of unmarked numbers equal to 148 for a final score of 148 * 13 = 1924.
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Figure out which board will win last. Once it wins, what would its final score be?
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Your puzzle answer was 2730.
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Both parts of this puzzle are complete! They provide two gold stars: **
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209
2021/day04/aoc-c.c
Normal file
209
2021/day04/aoc-c.c
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@@ -0,0 +1,209 @@
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/* aoc-c: Advent2021 game, day 2 parts 1 & 2
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*
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* Copyright (C) 2021 Bruno Raoult ("br")
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* Licensed under the GNU General Public License v3.0 or later.
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* Some rights reserved. See COPYING.
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*
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* You should have received a copy of the GNU General Public License along with this
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* program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.htmlL>.
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*
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* SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <malloc.h>
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#include "debug.h"
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#include "bits.h"
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#include "list.h"
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#include "pool.h"
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struct board {
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u16 win;
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u16 rcount[5];
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u16 ccount[5];
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int board[5][5];
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struct list_head list;
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};
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struct draw {
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u16 count;
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u16 *draw;
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} draw;
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LIST_HEAD(list_head);
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static int nboards = 0;
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static void read_draw()
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{
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char *buf = NULL, *token;
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size_t alloc = 0;
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ssize_t len;
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len = getline(&buf, &alloc, stdin);
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draw.draw = calloc(len/2, sizeof(*draw.draw));
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token = strtok(buf, ",\n");
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while (token) {
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draw.draw[draw.count++] = atoi(token);
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token = strtok(NULL, ",\n ");
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};
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free(buf);
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return;
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}
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#ifdef DEBUG
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static void print_boards()
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{
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int loop = 0, row, col;
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struct board *cur_board;
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list_for_each_entry(cur_board, &list_head, list) {
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printf("board %d\n", loop);
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for (row = 0; row < 5; ++row) {
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for (col = 0; col < 5; ++col) {
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printf("%d\t", cur_board->board[row][col]);
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}
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printf("\n");
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}
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++loop;
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}
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}
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#endif
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static struct list_head *read_boards()
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{
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char *buf = NULL;
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size_t alloc = 0;
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ssize_t len;
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static pool_t *pool;
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struct board dummy; /* for maybe-uninitialized warning */
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struct board *cur_board = &dummy;
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int row = 0;
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if (!(pool = pool_init("boards", 10, sizeof (struct board))))
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return NULL;
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while ((len = getline(&buf, &alloc, stdin)) >= 0) {
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/* skip blank lines */
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if (len == 1) {
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row = 0;
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continue;
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}
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if (row == 0) {
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nboards++;
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if (!(cur_board = pool_get(pool)))
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return NULL;
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for (int i = 0; i < 5; ++i) {
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cur_board->rcount[i] = 0;
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cur_board->ccount[i] = 0;
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cur_board->win = 0;
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}
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list_add_tail(&cur_board->list, &list_head);
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}
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sscanf(buf, "%d%d%d%d%d",
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&cur_board->board[row][0],
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&cur_board->board[row][1],
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&cur_board->board[row][2],
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&cur_board->board[row][3],
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&cur_board->board[row][4]);
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row++;
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}
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free(buf);
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return &list_head;
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}
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inline static int calc_board(struct board *board, int num)
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{
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int res = 0, row, col;
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for (row = 0; row < 5; ++row) {
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for (col = 0; col < 5; ++col) {
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if (board->board[row][col] > 0)
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res += board->board[row][col];
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}
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}
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return num * res;
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}
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inline static int check_win(int num, int part)
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{
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struct board *board;
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u32 row, col;
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static int nwins = 0;
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list_for_each_entry(board, &list_head, list) {
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if (board->win)
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continue;
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for (row = 0; row < 5; ++row) {
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for (col = 0; col < 5; ++col) {
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if (board->board[row][col] == num) {
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board->board[row][col] *= -1;
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board->rcount[row]++;
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board->ccount[col]++;
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if (board->rcount[row] == 5 || /* found */
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board->ccount[col] == 5) {
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board->win = 1;
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nwins++;
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if (part == 1 || nwins == nboards)
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return calc_board(board, num);
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}
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}
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}
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}
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}
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return -1;
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}
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static int doit(int part)
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{
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u32 num;
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int i, res;
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for (i = 0; i < draw.count; ++i) {
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num = draw.draw[i];
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if ((res = check_win(num, part)) > 0)
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return res;
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}
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return -1; /* impossible */
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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(int ac, char **av)
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{
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int opt;
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u32 exercise = 1, res;
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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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exercise = atoi(optarg);
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if (exercise < 1 || exercise > 2)
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return usage(*av);
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break;
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default:
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return usage(*av);
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}
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}
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if (optind < ac)
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return usage(*av);
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read_draw();
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read_boards();
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res = doit(exercise);
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printf ("%s : res=%d\n", *av, res);
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exit (0);
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}
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