From 985d8d2db0cb743f5fd1982b5c5af4615eb53931 Mon Sep 17 00:00:00 2001
From: Adam Spragg <adam@spra.gg>
Date: Wed, 28 Dec 2022 14:58:43 +0000
Subject: Solve puzzle 23 part 2

---
 23.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 47 insertions(+), 15 deletions(-)

(limited to '23.c')

diff --git a/23.c b/23.c
index 24d2c3d..99a3fb7 100644
--- a/23.c
+++ b/23.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 
 #define arrlen(x) (sizeof(x)/sizeof((x)[0]))
@@ -249,14 +250,36 @@ grid_dump(char * buf, int cols, int rows)
 
 
 int
-main()
+main(int argc, char ** argv)
 {
+	int rounds = 10;
 	char * buf = NULL, * pch;
 	int bufsiz = 0, buflen = 0;
 	int cols, rows, round;
 	int xmin, xmax, ymin, ymax, i, j;
 	int empty;
 
+	while ((i = getopt(argc, argv, "p:r:")) != -1) {
+		switch (i) {
+		case 'p':
+			switch (atoi(optarg)) {
+			case 1: rounds = 10; break;
+			case 2: rounds = -1; break;
+			default:
+				fprintf(stderr, "Unexpected part %s\n", optarg);
+				return -1;
+			}
+			break;
+
+		case 'r':
+			rounds = atoi(optarg);
+			break;
+
+		default:
+			return -1;
+		}
+	}
+
 	// Read input
 	while (1) {
 		size_t n;
@@ -294,9 +317,9 @@ main()
 	}
 
 	// Do rounds of movement simulation
-	for (round = 0; round < 10; ++round) {
+	for (round = 0; round < rounds || rounds < 0; ++round) {
 		char * psrc, * pdest;
-		int dir;
+		int dir, moves = 0;
 
 		// Get current bounding box.
 		if (bounding(&xmin, &xmax, &ymin, &ymax, buf, cols, rows) != 0) {
@@ -428,6 +451,7 @@ main()
 					pdest = posd(buf, cols, rows, i, j, dir);
 					*pdest = '#';
 					*psrc = '.';
+					++moves;
 				}
 				else if (loc_proposed(*psrc)) {
 					// Clean up count of elves who wanted to move here.
@@ -436,28 +460,36 @@ main()
 			}
 		}
 
+		if (!moves)
+			break;
+
 #if 0
 		fprintf(stderr, "Round %d\n", round + 1);
 		grid_dump(buf, cols, rows);
 #endif
 	}
 
-	// Find the number of empty cells in the bounding box
-	empty = 0;
-	if (bounding(&xmin, &xmax, &ymin, &ymax, buf, cols, rows) != 0) {
-		fprintf(stderr, "Can't find bounding box!\n");
-		free(buf);
-		return -1;
+	if (rounds < 0) {
+		printf("Number of rounds needed to stabilise: %d\n", round + 1);
 	}
-	for (j = ymin; j < ymax; ++j) {
-		for (i = xmin; i < xmax; ++i) {
-			if (loc_clear(*pos(buf, cols, rows, i, j))) {
-				++empty;
+	else {
+		// Find the number of empty cells in the bounding box
+		empty = 0;
+		if (bounding(&xmin, &xmax, &ymin, &ymax, buf, cols, rows) != 0) {
+			fprintf(stderr, "Can't find bounding box!\n");
+			free(buf);
+			return -1;
+		}
+		for (j = ymin; j < ymax; ++j) {
+			for (i = xmin; i < xmax; ++i) {
+				if (loc_clear(*pos(buf, cols, rows, i, j))) {
+					++empty;
+				}
 			}
 		}
-	}
 
-	printf("Number of empty spaces: %d\n", empty);
+		printf("Number of empty spaces after %d rounds: %d\n", rounds, empty);
+	}
 
 	// Tidy and exit
 	free(buf);
-- 
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