day 3

1 files changed, 65 insertions, 6 deletions

diff --git a/03.c b/03.c
index d783b79..738062c 100644
--- a/03.c
+++ b/03.c
@@ -1,12 +1,21 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <err.h>
+#include <stdbool.h>
 #include "input.h"
 
 #define INPUT "input/03.txt"
 #define INPUT_SIZE 12
 
-void part1(struct input_str* input) {
+unsigned long parse_line(char* binary_line, char expected_end) {
+	char* endp = NULL;
+	unsigned long result = strtoul(binary_line, &endp, 2);
+	if(*endp != expected_end)
+		err(1, "cannot parse line: %s\n", binary_line);
+	return result;
+}
+
+unsigned long compute_gamma(struct input_str* input) {
 	int oneCount[INPUT_SIZE];
 	// TODO is that necessary ?
 	for(int k = 0; k < INPUT_SIZE; k++) {
@@ -24,18 +33,67 @@ void part1(struct input_str* input) {
 	// null terminated string	
 	char binary[INPUT_SIZE + 1];
 	for(int h = 0; h < INPUT_SIZE; h++) {
-		binary[h] = oneCount[h] > input->line_count / 2.0f ? '1' : '0';
+		binary[h] = oneCount[h] >= input->line_count / 2.0f ? '1' : '0';
 	}
 	binary[INPUT_SIZE] = '\0';
-	char* endp = NULL;
-	unsigned long gamma = strtoul(binary, &endp, 2);
+	unsigned long gamma = parse_line(binary, '\0');
+	return gamma; 
+}
+
+unsigned long compute_epsilon(unsigned long gamma) {
 	unsigned long epsilon = gamma ^ 0xFFF;
-	if(*endp != '\0')
-		err(1, "erreur de parsing du gammaat");
+	return epsilon;
+}
 
+void part1(struct input_str* input) {
+	unsigned long gamma = compute_gamma(input);
+	unsigned long epsilon = compute_epsilon(gamma);
 	printf("%ld\n", gamma * epsilon);
 }
 
+unsigned long search_criteria(struct input_str* input, unsigned long criteria) {
+	unsigned long match;
+	bool foundLine = false;
+	unsigned long mask = 1 << (INPUT_SIZE - 1); // we start by checking only the first bit
+	for(int linePos = 0; linePos < INPUT_SIZE; linePos++) {
+		for(size_t is = 0; is < input->line_count; is++) {
+			// TODO this parsing step could be outside of this loop
+			unsigned long parsedLine = parse_line(input->lines[is], '\n');
+			if((parsedLine & mask) == (criteria & mask)) {
+				// this line fits the criteria
+				if(foundLine) {
+					// more than one line fits, we need to consider another bit
+					foundLine = false;
+					mask = (mask >> 1) | (1 << (INPUT_SIZE - 1));
+					break;
+				}
+				else {
+					// save it for later
+					foundLine = true;
+					match = parsedLine;
+				}
+			}
+		}
+
+		// checked all lines, if we found one matching then it is the one we want
+		if(foundLine)
+			break;
+	}
+
+	if(!foundLine)
+		err(1, "cannot find line matching mask %ld\n", mask);
+
+	return match;
+}
+
+void part2(struct input_str* input) {
+	unsigned long o2_criteria = compute_gamma(input);
+	unsigned long o2_rate = search_criteria(input, o2_criteria);
+	unsigned long co2_criteria = compute_epsilon(o2_criteria);
+	unsigned long co2_scrub = search_criteria(input, co2_criteria);
+	printf("%ld\n", o2_rate * co2_scrub);
+}
+
 int main() {
 	// read input data
 	struct input_str input;
@@ -43,6 +101,7 @@ int main() {
 
 	// do stuff
 	part1(&input);
+	part2(&input);
 
 	// cleanup & exit
 	input_str_free(&input);