Initial commit

3 files changed, 39 insertions, 0 deletions

diff --git a/2020/15/.gitignore b/2020/15/.gitignore
new file mode 100644
index 0000000..60d075d
--- /dev/null
+++ b/2020/15/.gitignore
@@ -0,0 +1 @@
+puzzle-[12]
diff --git a/2020/15/Makefile b/2020/15/Makefile
new file mode 100644
index 0000000..c32dafa
--- /dev/null
+++ b/2020/15/Makefile
@@ -0,0 +1,7 @@
+all:
+	${CC} ${CFLAGS} -o puzzle-1 puzzles.c
+	${CC} ${CFLAGS} -DPART2 -o puzzle-2 puzzles.c
+
+.PHONY: clean
+clean:
+	rm -f puzzle-[12]
diff --git a/2020/15/puzzles.c b/2020/15/puzzles.c
new file mode 100644
index 0000000..64d89bb
--- /dev/null
+++ b/2020/15/puzzles.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifndef PART2
+	#define BUFFER 2020
+#else
+	#define BUFFER 30000000
+#endif
+
+int
+main(void)
+{
+	/* Given starting numbers */
+	static unsigned int nums[BUFFER] = {0};
+	nums[6] = 1;
+	nums[19] = 2;
+	nums[0] = 3;
+	nums[5] = 4;
+	nums[7] = 5;
+	nums[13] = 6;
+
+	unsigned int temp, lnum = 1;
+	for (int i = 8; i <= BUFFER; i++) {
+		temp = lnum;
+		lnum = nums[lnum] ? i - 1 - nums[lnum] : 0;
+		nums[temp] = i - 1;
+	}
+
+	printf("%u\n", lnum);
+	return EXIT_SUCCESS;
+}