2019 day 8: parts 1 & 2

2019/day08/EXAMPLE.txt

@@ -1 +1 @@
-123456789012
+0222112222120000

2019/day08/README.org

@@ -43,10 +43,57 @@ would like you to find the layer that contains the /fewest =0= digits/.
 On that layer, what is /the number of =1= digits multiplied by the
 number of =2= digits?/
 
-To begin, [[file:8/input][get your puzzle input]].
+Your puzzle answer was =2250=.
 
-Answer:
+** --- Part Two ---
+Now you're ready to decode the image. The image is rendered by stacking
+the layers and aligning the pixels with the same positions in each
+layer. The digits indicate the color of the corresponding pixel: =0= is
+black, =1= is white, and =2= is transparent.
 
-You can also [Shareon
-[[https://twitter.com/intent/tweet?text=%22Space+Image+Format%22+%2D+Day+8+%2D+Advent+of+Code+2019&url=https%3A%2F%2Fadventofcode%2Ecom%2F2019%2Fday%2F8&related=ericwastl&hashtags=AdventOfCode][Twitter]]
-[[javascript:void(0);][Mastodon]]] this puzzle.
+The layers are rendered with the first layer in front and the last layer
+in back. So, if a given position has a transparent pixel in the first
+and second layers, a black pixel in the third layer, and a white pixel
+in the fourth layer, the final image would have a /black/ pixel at that
+position.
+
+For example, given an image =2= pixels wide and =2= pixels tall, the
+image data =0222112222120000= corresponds to the following image layers:
+
+#+BEGIN_EXAMPLE
+  Layer 1: 02
+           22
+
+  Layer 2: 11
+           22
+
+  Layer 3: 22
+           12
+
+  Layer 4: 00
+           00
+#+END_EXAMPLE
+
+Then, the full image can be found by determining the top visible pixel
+in each position:
+
+- The top-left pixel is /black/ because the top layer is =0=.
+- The top-right pixel is /white/ because the top layer is =2=
+  (transparent), but the second layer is =1=.
+- The bottom-left pixel is /white/ because the top two layers are =2=,
+  but the third layer is =1=.
+- The bottom-right pixel is /black/ because the only visible pixel in
+  that position is =0= (from layer 4).
+
+So, the final image looks like this:
+
+#+BEGIN_EXAMPLE
+  01
+  10
+#+END_EXAMPLE
+
+/What message is produced after decoding your image?/
+
+Your puzzle answer was =FHJUL=.
+
+Both parts of this puzzle are complete! They provide two gold stars: **

2019/day08/aoc-c.c

@@ -0,0 +1,120 @@
+/* aoc-c.c: Advent of Code 2019, day 8 parts 1 & 2
+ *
+ * Copyright (C) 2022 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+#include "br.h"
+#include "bits.h"
+#include "debug.h"
+#include "list.h"
+#include "pool.h"
+
+struct input {
+    int len;
+    char *buf;
+
+};
+
+static int part1(struct input *input, int width, int height)
+{
+    int depth = input->len / width / height;
+    int minzero = input->len, n1n2;
+
+    for (int i = 0; i < depth; ++i) {
+        char *layer = input->buf + i * (width * height);
+        int tmp[10] = {0};
+        for (int j = 0; j < width*height; ++j) {
+            tmp[layer[j] - '0'] ++;
+        }
+        if (tmp[0] < minzero) {
+            minzero = tmp[0];
+            n1n2 = tmp[1] * tmp[2];
+        }
+    }
+    return n1n2;
+}
+
+static int part2(struct input *input, int width, int height)
+{
+    for (int line = 0; line < height; line++) {
+        for (int pixel = 0; pixel < width; ++pixel) {
+            char *pos = input->buf + line * width + pixel;
+            while (pos < input->buf + input->len && *pos == '2')
+                pos += width * height;
+            putchar(*pos == '0'? ' ': '#');
+        }
+        putchar('\n');
+    }
+    return 0;
+}
+
+static int parse(struct input *input)
+{
+    size_t alloc = 0;
+    ssize_t buflen;
+    char *buf = NULL;
+
+    if ((buflen = getline(&buf, &alloc, stdin)) <= 0) {
+        fprintf(stderr, "error reading file.\n");
+        return 0;
+    }
+    buf[buflen--] = 0;
+    input->buf = buf;
+    input->len = buflen;
+    return buflen;
+}
+
+static int usage(char *prg)
+{
+    fprintf(stderr, "Usage: %s [-d debug_level] [-p part] [-i input]\n", prg);
+    return 1;
+}
+
+int main(int ac, char **av)
+{
+    int opt, part = 1, width = 25, height = 6;
+    struct input input = { 0 };
+
+    while ((opt = getopt(ac, av, "d:p:w:h:")) != -1) {
+        switch (opt) {
+            case 'd':
+                debug_level_set(atoi(optarg));
+                break;
+            case 'w':
+                width = atoi(optarg);
+                break;
+            case 'h':
+                height = atoi(optarg);
+                break;
+            case 'p':                             /* 1 or 2 */
+                part = atoi(optarg);
+                if (part < 1 || part > 2)
+                    return usage(*av);
+                break;
+            default:
+                return usage(*av);
+        }
+    }
+    if (optind < ac)
+        return usage(*av);
+
+    parse(&input);
+    printf("%s : res=%d\n", *av,
+           part == 1?
+           part1(&input, width, height) :
+           part2(&input, width, height));
+    free(input.buf);
+    exit(0);
+}