Initial commit

1 files changed, 126 insertions, 0 deletions

diff --git a/2020/18/puzzles.c b/2020/18/puzzles.c
new file mode 100644
index 0000000..5afbe00
--- /dev/null
+++ b/2020/18/puzzles.c
@@ -0,0 +1,126 @@
+#define _GNU_SOURCE
+#include <sys/types.h>
+
+#include <ctype.h>
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static unsigned long long parse_number(void);
+static unsigned long long parse_digit(void);
+static unsigned long long parse_result(void);
+
+#ifdef PART2
+static unsigned long long parse_sum(void);
+static unsigned long long parse_product(void);
+#endif
+
+char *g_current;
+
+/* Convert the current number from a string to an int */
+unsigned long long
+parse_number(void)
+{
+	unsigned long long number = 0;
+	while (isdigit(*g_current))
+		number = number * 10 + *g_current++ - '0';
+
+	return number;
+}
+
+/* Parse the current digit pointed to by `g_current` */
+unsigned long long
+parse_digit(void)
+{
+	if (isdigit(*g_current))
+		return parse_number();
+
+	/* If not a digit, it's a parenthesis */
+	g_current++;
+	unsigned long long result = parse_result();
+	g_current++;
+	return result;
+}
+
+#ifdef PART2
+/* Parse and compute a sum */
+unsigned long long
+parse_sum(void)
+{
+	unsigned long long result = parse_digit();
+
+	while (*g_current == '+') {
+		g_current++;
+		result += parse_digit();
+	}
+
+	return result;
+}
+
+/* Parse and compute a product */
+unsigned long long
+parse_product(void)
+{
+	unsigned long long result = parse_sum();
+
+	while (*g_current == '*') {
+		g_current++;
+		result *= parse_sum();
+	}
+
+	return result;
+}
+#endif
+
+/* Parse and compute a sum */
+unsigned long long
+parse_result(void)
+{
+#ifdef PART2
+	return parse_product();
+#else
+	unsigned long long result = parse_digit();
+
+	while (*g_current == '+' || *g_current == '*') {
+		if (*g_current++ == '+')
+			result += parse_digit();
+		else
+			result *= parse_digit();
+	}
+
+	return result;
+#endif
+}
+
+/* Remove the spaces from user input */
+static void
+remove_spaces(char *str)
+{
+	char const *c = str;
+	do
+		while (*c == ' ')
+			c++;
+	while ((*str++ = *c++));
+}
+
+int
+main(void)
+{
+	FILE *fp;
+	char *line = NULL;
+	size_t len = 0;
+	ssize_t read;
+
+	if (!(fp = fopen("input", "r")))
+		err(EXIT_FAILURE, "fopen");
+
+	unsigned long long acc = 0;
+	while ((read = getline(&line, &len, fp)) != -1) {
+		remove_spaces(line);
+		g_current = line;
+		acc += parse_result();
+	}
+
+	printf("%llu\n", acc);
+	return EXIT_SUCCESS;
+}