Very inefficient solution (hashmap?)

3 files changed, 56 insertions, 0 deletions

diff --git a/2020/15/Makefile b/2020/15/Makefile
new file mode 100644
index 0000000..9c7ab36
--- /dev/null
+++ b/2020/15/Makefile
@@ -0,0 +1,10 @@
+.PHONY: solve.c
+
+solve.o: solve.c
+	@gcc -g -Ofast $+ -o $@
+
+clean:
+	@rm -f *.o
+
+run: solve.o
+	@./solve.o
diff --git a/2020/15/input b/2020/15/input
new file mode 100644
index 0000000..909319b
--- /dev/null
+++ b/2020/15/input
@@ -0,0 +1 @@
+19,20,14,0,9,1
diff --git a/2020/15/solve.c b/2020/15/solve.c
new file mode 100644
index 0000000..0707208
--- /dev/null
+++ b/2020/15/solve.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define MAX_NUMS 30000000
+
+static int nums[MAX_NUMS] = { 0 };
+
+int part_one(FILE *fp, int count)
+{
+	long size = 0;
+	while (size < count)
+		if (fscanf(fp, "%d,", &nums[size++]) != 1)
+			break;
+
+	for (int i = size - 2; i < count - 1; i++) {
+		for (int j = i - 1; j >= 0; j--) {
+			if (nums[j] == nums[i]) {
+				nums[i + 1] = i - j;
+				break;
+			}
+		}
+	}
+
+	return nums[count - 1];
+}
+
+int main(int argc, char *argv[])
+{
+	FILE *fp = fopen("input", "r");
+	if (!fp)
+		exit(EXIT_FAILURE);
+
+	clock_t tic = clock();
+	printf("%d\n", part_one(fp, 2020));
+	memset(nums, 0, 2020);
+	rewind(fp);
+	printf("%d\n", part_one(fp, 30000000));
+	clock_t toc = clock();
+	printf("TIME: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
+
+	fclose(fp);
+	return 0;
+}