1 files changed, 165 insertions, 0 deletions
diff --git a/02.c b/02.c
new file mode 100644
index 0000000..8ca0423
--- /dev/null
+++ b/02.c
@@ -0,0 +1,165 @@
+#include "input.h"
+
+#include <stddef.h>
+#include <stdio.h>
+#include <err.h>
+
+#define INPUT "input/02.txt"
+#define EXPECTED1 13221L
+#define EXPECTED2 13131L
+
+enum draw {
+	rock = 1,
+	paper = 2,
+	scissors = 3,
+};
+
+struct round_p1 {
+	enum draw opponent;
+	enum draw me;
+};
+
+int compute_round_score_p1(struct round_p1* round) {
+	int score = (int) round->me;
+	enum draw opponent = round->opponent;
+	enum draw me = round->me;
+	if((opponent == rock && me == paper) || (opponent == paper && me == scissors) || (opponent == scissors && me == rock))
+		score += 6; // win
+	else if(opponent == me)
+		score += 3; // draw
+	// loss is 0
+	return score;
+}
+
+void parse_round_p1(struct round_p1* round, char* round_str) {
+	switch(round_str[0]) {
+		case 'A':
+			round->opponent = rock;
+			break;
+		case 'B':
+			round->opponent = paper;
+			break;
+		case 'C':
+			round->opponent = scissors;
+			break;
+		default:
+			err(2, "unknown opponent choice %c", round_str[0]);
+	}
+	switch(round_str[2]) {
+		case 'X':
+			round->me = rock;
+			break;
+		case 'Y':
+			round->me = paper;
+			break;
+		case 'Z':
+			round->me = scissors;
+			break;
+		default:
+			err(2, "unknown me choice %c", round_str[2]);
+	}
+}
+
+void part1(struct input_str* input) {
+	// compute max calories
+	long score = 0;
+	struct round_p1 r;
+	for(size_t i = 0; i < input->line_count; i++) {
+		parse_round_p1(&r, input->lines[i]);
+		int round_score = compute_round_score_p1(&r);
+		score += round_score;
+	}
+
+	CHECK(score, EXPECTED1)
+}
+
+enum round_result {
+	loss = 0,
+	draw = 3,
+	win = 6,
+};
+
+struct round_p2 {
+	enum draw opponent;
+	enum round_result result;
+};
+
+int compute_round_score_p2(struct round_p2* round) {
+	enum draw opponent = round->opponent;
+	enum round_result result = round->result;
+	enum draw me;
+	switch(result) {
+		case loss:
+			if(opponent == rock)
+				me = scissors;
+			else
+				me = (enum draw) ((int) opponent - 1);
+			break;
+		case draw:
+			me = opponent;
+			break;
+		case win:
+			if(opponent == scissors)
+				me = rock;
+			else
+				me = (enum draw) ((int) opponent + 1);
+			break;
+	}
+	return (int) me + (int) result;
+}
+
+void parse_round_p2(struct round_p2* round, char* round_str) {
+	switch(round_str[0]) {
+		case 'A':
+			round->opponent = rock;
+			break;
+		case 'B':
+			round->opponent = paper;
+			break;
+		case 'C':
+			round->opponent = scissors;
+			break;
+		default:
+			err(2, "unknown opponent choice %c", round_str[0]);
+	}
+	switch(round_str[2]) {
+		case 'X':
+			round->result = loss;
+			break;
+		case 'Y':
+			round->result = draw;
+			break;
+		case 'Z':
+			round->result = win;
+			break;
+		default:
+			err(2, "unknown expected result %c", round_str[2]);
+	}
+}
+
+void part2(struct input_str* input) {
+	// compute max calories
+	long score = 0;
+	struct round_p2 r;
+	for(size_t i = 0; i < input->line_count; i++) {
+		parse_round_p2(&r, input->lines[i]);
+		int round_score = compute_round_score_p2(&r);
+		score += round_score;
+	}
+
+	CHECK(score, EXPECTED2)
+}
+
+int main() {
+	// read input
+	struct input_str input;
+	input_str_read(&input, INPUT);
+
+	// do stuff
+	part1(&input);
+	part2(&input);
+
+	// cleanup & exit
+	input_str_free(&input);
+	return 0;
+}