Solve puzzle 17 part 1

1 files changed, 173 insertions, 0 deletions

diff --git a/17.c b/17.c
new file mode 100644
index 0000000..67230fb
--- /dev/null
+++ b/17.c
@@ -0,0 +1,173 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+#define arrlen(x) (sizeof(x)/sizeof((x)[0]))
+
+
+struct rock {
+	unsigned char s[4];
+};
+
+
+struct rock const rocks[] = {
+	{ { 0x1e, 0, 0, 0 } },		// Horizontal line
+	{ { 0x08, 0x1c, 0x08, 0 } },	// Cross
+	{ { 0x1c, 0x04, 0x04, 0 } },	// Elbow
+	{ { 0x10, 0x10, 0x10, 0x10 } },	// Line piece
+	{ { 0x18, 0x18, 0, 0 } },	// Block
+};
+
+
+#if 0
+void
+chamber_dump(unsigned char * chamber, int chamberheight, struct rock * rock, int rockheight)
+{
+	int i;
+
+	for (i = chamberheight - 1; i >= 0; --i) {
+		unsigned char c;
+
+		fputc('|', stderr);
+
+		for (c = 0x40; c != 0; c >>= 1) {
+			if (rock && i >= rockheight
+					&& i < rockheight + arrlen(rock->s)
+					&& (rock->s[i - rockheight] & c))
+				fputc('@', stderr);
+			else if (chamber && (chamber[i] & c))
+				fputc('#', stderr);
+			else
+				fputc('.', stderr);
+		}
+
+
+		fputc('|', stderr);
+		fputc('\n', stderr);
+	}
+	fprintf(stderr, "+-------+\n");
+}
+#endif
+
+
+int
+main()
+{
+	size_t jetsize = 0;
+	char * jets = NULL;
+	unsigned char * chamber = NULL;
+	int chamberheight = 0, top = 0;
+	int movement, rocknum, rockheight;
+	struct rock rock;
+	int i;
+
+	// Read jets.
+	while (1) {
+		void * p;
+		size_t s;
+
+		if ((p = realloc(jets, jetsize + BUFSIZ)) == NULL) {
+			fprintf(stderr, "jets: bad realloc (%zu)\n", jetsize + BUFSIZ);
+			free(jets);
+			return -1;
+		}
+		jets = p;
+		if ((s = fread(jets + jetsize, 1, BUFSIZ, stdin)) == 0)
+			break;
+		jetsize += s;
+	}
+
+	// Remove any characters that are not '<' or '>' (e.g. newlines)
+	for (i = 0; i < jetsize; ++i) {
+		while (i < jetsize && jets[i] != '<' && jets[i] != '>') {
+			memmove(jets + i, jets + i + 1, jetsize - (i + 1));
+			--jetsize;
+		}
+	}
+
+	// Place first rock, and start movement
+	rocknum = 0;
+	rock = rocks[rocknum];
+	rockheight = 3;
+
+	for (movement = 0; rocknum < 2022; ++movement) {
+		int jet;
+
+		if (top > chamberheight - 10) {
+			void * p;
+
+			if ((p = realloc(chamber, chamberheight + BUFSIZ)) == NULL) {
+				fprintf(stderr, "Bad realloc(%d)\n", chamberheight + BUFSIZ);
+				free(chamber);
+				return -1;
+			}
+			chamber = p;
+			memset(chamber + chamberheight, 0, BUFSIZ);
+			chamberheight += BUFSIZ;
+		}
+
+		jet = jets[movement % jetsize];
+
+		// Check if jet can push rock.
+		for (i = 0; i < arrlen(rock.s); ++i) {
+			// Check left wall collision
+			if (jet == '<' && (rock.s[i] & 0x40) != 0)
+				jet = 0;
+
+			// Check right wall collision
+			if (jet == '>' && (rock.s[i] & 0x01) != 0)
+				jet = 0;
+
+			// Check moving left into existing rocks.
+			if (jet == '<' && ((rock.s[i] << 1) & chamber[rockheight + i]) != 0)
+				jet = 0;
+
+			// Check moving right into existing rocks
+			if (jet == '>' && ((rock.s[i] >> 1) & chamber[rockheight + i]) != 0)
+				jet = 0;
+		}
+
+		// If jet can push rock, do so.
+		if (jet == '<')
+			for (i = 0; jet && i < arrlen(rock.s); ++i)
+				rock.s[i] <<= 1;
+		if (jet == '>')
+			for (i = 0; jet && i < arrlen(rock.s); ++i)
+				rock.s[i] >>= 1;
+
+		// Check if rock can fall.
+		for (i = 0; rockheight > 0 && i < arrlen(rock.s); ++i)
+			if ((rock.s[i] & chamber[rockheight - 1 + i]) != 0)
+				break;
+		if (i < arrlen(rock.s)) {
+			// Rock cannot fall. Place rock.
+			for (i = 0; i < arrlen(rock.s) && rock.s[i] != 0; ++i) {
+				chamber[rockheight + i] |= rock.s[i];
+				if (rockheight + i > top)
+					top = rockheight + i;
+			}
+
+			// Pick next rock.
+			rock = rocks[++rocknum % arrlen(rocks)];
+			rockheight = top + 4;
+
+#if 0
+			chamber_dump(chamber, top + 7, &rock, rockheight);
+#endif
+		}
+		else {
+			// Rock can fall, so reduce its height by 1
+			--rockheight;
+		}
+	}
+
+	printf("Height of rocks in chamber: %d\n", top + 1);
+
+	free(chamber);
+	free(jets);
+
+	return 0;
+}
+