From 631fe6892464c8b41cbff5ee1785ade2c24986c6 Mon Sep 17 00:00:00 2001
From: Adam Spragg <adam@spra.gg>
Date: Thu, 8 Dec 2022 18:34:30 +0000
Subject: Solve puzzle 8 part 2

---
 8.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 2 deletions(-)

diff --git a/8.c b/8.c
index aa46ec4..a400462 100644
--- a/8.c
+++ b/8.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 
 // Check if a tree is newly seen, by being taller than max or not
@@ -65,12 +66,65 @@ forest_seen(unsigned char * forest, int rows, int cols)
 }
 
 
+// Get the maximum scenic score for a tree
 int
-main()
+forest_maxscore(unsigned char * forest, int rows, int cols)
 {
+	int i, j, max = 0;
+
+	for (i = 1; i < rows - 1; ++i) {
+		for (j = 1; j < cols - 2; ++j) {
+			int dist;
+			int score = 1;
+			int height = forest[i * cols + j];
+
+			for (dist = 1; j - dist > 0; ++dist)
+				if (forest[i * cols + j - dist] >= height)
+					break;
+			score *= dist;
+
+			for (dist = 1; j + dist < cols - 2; ++dist)
+				if (forest[i * cols + j + dist] >= height)
+					break;
+			score *= dist;
+
+			for (dist = 1; i - dist > 0; ++dist)
+				if (forest[(i - dist) * cols + j] >= height)
+					break;
+			score *= dist;
+
+			for (dist = 1; i + dist < rows - 1; ++dist)
+				if (forest[(i + dist) * cols + j] >= height)
+					break;
+			score *= dist;
+
+			if (score > max)
+				max = score;
+		}
+	}
+
+	return max;
+}
+
+
+int
+main(int argc, char ** argv)
+{
+	int i, part = 1;
 	int cols = 0, rows = 0;
 	char * forest;
 
+	while ((i = getopt(argc, argv, "p:")) != -1) {
+		switch (i) {
+		case 'p':
+			part = atoi(optarg);
+			break;
+
+		default:
+			return -1;
+		}
+	}
+
 	// Read first line
 	forest = malloc(BUFSIZ);
 	if (!fgets(forest, BUFSIZ, stdin)) {
@@ -115,7 +169,22 @@ main()
 		++rows;
 	}
 
-	printf("Trees seen: %d\n", forest_seen((unsigned char *) forest, rows, cols));
+	switch (part) {
+	case 1:
+		printf("Trees seen: %d\n",
+				forest_seen((unsigned char *) forest, rows, cols));
+		break;
+
+	case 2:
+		printf("Best visibility: %d\n",
+				forest_maxscore((unsigned char *) forest, rows, cols));
+		break;
+
+	default:
+		fprintf(stderr, "Unexpected part %d\n", part);
+		free(forest);
+		return -1;
+	}
 
 	free(forest);
 
-- 
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