diff --git a/3/3-1.c b/3/3-1.c
new file mode 100644
index 0000000..fea17e2
--- /dev/null
+++ b/3/3-1.c
@@ -0,0 +1,45 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+#define WIDTH 5
+
+int main(int argc, char const *argv[])
+{
+    FILE *p_file = fopen("input", "r");
+
+    uint n_one[WIDTH] = {0};
+    uint length = 0;
+
+    char line[WIDTH + 2];
+    while (fgets(line, sizeof line, p_file) != NULL)
+    {
+        length++;
+        for (size_t i = 0; i < WIDTH; i++)
+        {
+            if (line[i] - '0') // 1
+            {
+                n_one[i]++;
+            }
+        }
+    }
+
+    // GET GAMMA/EPSILON
+    uint gamma = 0, epsilon = 0;
+    uint place = 1;
+    for (size_t i = WIDTH; i--;)
+    {
+        if (n_one[i] > length / 2)
+        {
+            gamma += place;
+        }
+        else
+        {
+            epsilon += place;
+        }
+        place *= 2;
+    }
+
+    printf("%d\n", gamma * epsilon);
+
+    return 0;
+}
diff --git a/3/3-2.c b/3/3-2.c
new file mode 100644
index 0000000..64abf82
--- /dev/null
+++ b/3/3-2.c
@@ -0,0 +1,127 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+#include "../check_alloc.h"
+
+#define INPUT_PATH "input"
+#define WIDTH 12
+
+// LIST DATASTRUCTURE
+#define INITIAL_SIZE 20
+
+typedef struct
+{
+    char **list;
+    size_t size;
+    size_t capacity;
+} LIST;
+
+void free_list(LIST *list)
+{
+    free(list->list);
+    free(list);
+}
+void delete_list(LIST *list)
+{
+    for (size_t i = 0; i < list->size; i++)
+    {
+        free(list->list[i]);
+    }
+    free_list(list);
+}
+
+LIST *new_list(void)
+{
+    LIST *p_list = calloc(1, sizeof(LIST));
+    p_list->capacity = INITIAL_SIZE;
+    p_list->list = calloc(p_list->capacity, sizeof(char *));
+    return p_list;
+}
+
+void add_list(LIST *list, char *elem)
+{
+    if (list->size >= list->capacity)
+    {
+        list->capacity *= 2;
+        list->list = realloc(list->list, list->capacity * sizeof(char *));
+        CHECK_ALLOC(list->list);
+    }
+    list->list[list->size] = elem;
+    list->size++;
+}
+
+//
+
+LIST *read_file(char *path)
+{
+    FILE *p_file = fopen(path, "r");
+    LIST *p_list = new_list();
+    char line[WIDTH + 2];
+    while (fgets(line, sizeof line, p_file) != NULL)
+    {
+        add_list(p_list, strdup(line));
+    }
+    return p_list;
+}
+
+char common_value(LIST *list, char index)
+{
+    uint one = 0;
+    uint zero = 0;
+    for (size_t i = 0; i < list->size; i++)
+    {
+        if (list->list[i][index] - '0')
+        {
+            one++;
+        }
+        else
+        {
+            zero++;
+        }
+    }
+    return one >= zero;
+}
+
+void partition(LIST *list, char index, bool co2, bool o2)
+{
+    if (index >= WIDTH || list->size == 1)
+    {
+        if (co2)
+            printf("CO2\n");
+        else
+            printf("O2\n");
+        printf("%lu\n", strtol(list->list[0], NULL, 2));
+        return;
+    }
+    char common = common_value(list, index);
+    LIST *p_list_co2 = new_list();
+    LIST *p_list_o2 = new_list();
+    for (size_t i = 0; i < list->size; i++)
+    {
+        if ((list->list[i][index] - '0') == common)
+        {
+            if (o2)
+                add_list(p_list_o2, list->list[i]);
+        }
+        else
+        {
+            if (co2)
+                add_list(p_list_co2, list->list[i]);
+        }
+    }
+    if (o2)
+        partition(p_list_o2, index + 1, false, true);
+    if (co2)
+        partition(p_list_co2, index + 1, true, false);
+    free_list(p_list_o2);
+    free_list(p_list_co2);
+}
+
+int main(int argc, char const *argv[])
+{
+    LIST *list = read_file(INPUT_PATH);
+    partition(list, 0, true, true);
+    delete_list(list);
+    return 0;
+}
diff --git a/check_alloc.h b/check_alloc.h
new file mode 100644
index 0000000..9c2384e
--- /dev/null
+++ b/check_alloc.h
@@ -0,0 +1,9 @@
+#include <stdlib.h>
+
+#ifndef CHECK_ALLOC
+#define CHECK_ALLOC(v)      \
+    if ((v) == NULL)        \
+    {                       \
+        exit(EXIT_FAILURE); \
+    }
+#endif
\ No newline at end of file