diff --git a/Makefile b/Makefile
index 6735525..0488875 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-main: main.c
+main: main.c day*.c
 	gcc -o main main.c -lcurl
 
 run: main
diff --git a/day1.c b/day1.c
index bbe46c1..3a0ab90 100644
--- a/day1.c
+++ b/day1.c
@@ -16,7 +16,8 @@ typedef struct {
 	size_t count;
 } Data;
 
-static void *day1_parse(char **lines, int line_count) {
+static void *day1_parse(char **lines, int line_count)
+{
 	int elf_indexes[300] = { 0 };
 	int elf_count = 1;
 	for (int i = 1; i < line_count; i++) {
@@ -45,7 +46,8 @@ static void *day1_parse(char **lines, int line_count) {
 	return data;
 }
 
-static int day1_part1(void *p) {
+static int day1_part1(void *p)
+{
 	Data *data = (Data*)p;
 	int max_calories = 0;
 	for (int i = 0; i < data->count; i++) {
@@ -58,7 +60,8 @@ static int day1_part1(void *p) {
 	return max_calories;
 }
 
-static int day1_part2(void *p) {
+static int day1_part2(void *p)
+{
 	Data *data = (Data*)p;
 	int max_calories1 = 0;
 	int max_calories2 = 0;
diff --git a/day2.c b/day2.c
index 8a0ec4b..708c29a 100644
--- a/day2.c
+++ b/day2.c
@@ -12,7 +12,8 @@ typedef struct {
 	size_t count;
 } day2_Data;
 
-static void *day2_parse(char **lines, int line_count) {
+static void *day2_parse(char **lines, int line_count)
+{
 	day2_Data *data = calloc(1, sizeof(day2_Data));
 	data->count = line_count;
 	data->rounds = calloc(line_count, sizeof(Round));
@@ -25,7 +26,8 @@ static void *day2_parse(char **lines, int line_count) {
 	return data;
 }
 
-static int day2_part1(void *p) {
+static int day2_part1(void *p)
+{
 	day2_Data *data = (day2_Data*)p;
 	int result = 0;
 	for (int i = 0; i < data->count; i++) {
@@ -54,7 +56,8 @@ static int day2_part1(void *p) {
 	return result;
 }
 
-static int day2_part2(void *p) {
+static int day2_part2(void *p)
+{
 	day2_Data *data = (day2_Data*)p;
 	int result = 0;
 	for (int i = 0; i < data->count; i++) {
diff --git a/day3.c b/day3.c
new file mode 100644
index 0000000..18b3bc6
--- /dev/null
+++ b/day3.c
@@ -0,0 +1,103 @@
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "aoc.h"
+
+typedef struct {
+	char *contents;
+	size_t size;
+} Backpack;
+
+typedef struct {
+	Backpack *backpacks;
+	size_t count;
+} day3_Data;
+
+static void *day3_parse(char **lines, int line_count)
+{
+	day3_Data *data = calloc(1, sizeof(day3_Data));
+	Backpack *backpacks = calloc(line_count, sizeof(Backpack));
+	data->backpacks = backpacks;
+	data->count = line_count;
+	for (size_t i = 0; i < line_count; i++) {
+		backpacks[i].size = strlen(lines[i]);
+		backpacks[i].contents = lines[i];
+	}
+	return data;
+}
+
+static bool contains(char needle, char* haystack, size_t len)
+{
+	for (size_t i = 0; i < len; i++) {
+		if (haystack[i] == needle) {
+			return true;
+		}
+	}
+	return false;
+}
+
+static char find_common(char *str1, char* str2, size_t len)
+{
+	for (size_t i = 0; i < len; i++) {
+		if (contains(str1[i], str2, len)) {
+			return str1[i];
+		}
+	}
+	return 0;
+}
+
+static int get_priority(char c)
+{
+		if ('a' <= c && c <= 'z') {
+			return (c - 'a') + 1;
+		} else if ('A' <= c && c <= 'Z') {
+			return (c - 'A') + 27;
+		}
+		return 0;
+}
+
+static int day3_part1(void *p)
+{
+	day3_Data *data = (day3_Data*)p;
+	int result = 0;
+	for (size_t i = 0; i < data->count; i++) {
+		Backpack *b = &data->backpacks[i];
+		char common = find_common(b->contents, b->contents+b->size/2, b->size/2);
+		if (common) {
+			result += get_priority(common);
+		} else {
+			fprintf(stderr, "Unknown common char at line: %zu\n", i+1);
+		}
+	}
+	return result;
+}
+
+static int day3_part2(void *p)
+{
+	day3_Data *data = (day3_Data*)p;
+	int result = 0;
+	for (size_t i = 0; i < data->count; i+=3) {
+		Backpack *b1 = &data->backpacks[i+0];
+		Backpack *b2 = &data->backpacks[i+1];
+		Backpack *b3 = &data->backpacks[i+2];
+
+		bool found = false;
+		for (size_t j = 0; j < b1->size; j++) {
+			char c = b1->contents[j];
+			if (contains(c, b2->contents, b2->size) && contains(c, b3->contents, b3->size)) {
+				result += get_priority(c);
+				found = true;
+				break;
+			}
+		}
+
+		if (!found) {
+			fprintf(stderr, "Unknown common char at line: %zu-%zu\n", i+1, i+3);
+		}
+	}
+	return result;
+}
+
+ADD_SOLUTION(3, day3_parse, day3_part1, day3_part2);
diff --git a/main.c b/main.c
index 8827f4f..2d385ac 100644
--- a/main.c
+++ b/main.c
@@ -10,6 +10,7 @@
 
 #include "day1.c"
 #include "day2.c"
+#include "day3.c"
 
 Solution *find_solution(int day)
 {