diff --git a/4/4-1.c b/4/4-1.c
new file mode 100644
index 0000000..0403cfd
--- /dev/null
+++ b/4/4-1.c
@@ -0,0 +1,162 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+#define BOARD_SIZE 5
+#define BOARD_BUF_SIZ 100
+
+typedef struct
+{
+    bool **state;
+    unsigned int **value;
+    unsigned int *column_done;
+    unsigned int *row_done;
+} BINGO_BOARD;
+
+BINGO_BOARD *new_bingo_board()
+{
+    BINGO_BOARD *p_board = calloc(1, sizeof(BINGO_BOARD));
+    p_board->column_done = calloc(BOARD_SIZE, sizeof(unsigned int));
+    p_board->row_done = calloc(BOARD_SIZE, sizeof(unsigned int));
+
+    p_board->state = calloc(BOARD_SIZE, sizeof(bool *));
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        p_board->state[i] = calloc(BOARD_SIZE, sizeof(bool));
+    }
+    p_board->value = calloc(BOARD_SIZE, sizeof(unsigned int *));
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        p_board->value[i] = calloc(BOARD_SIZE, sizeof(unsigned int));
+    }
+    return p_board;
+}
+
+void print_board(BINGO_BOARD *board)
+{
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            printf("%i(%i)\t", board->value[i][j], board->state[i][j]);
+        }
+        putchar('\n');
+    }
+}
+
+void *fill_bingo_board_row(BINGO_BOARD *board, char *line, char row)
+{
+    char *num_str = strtok(line, " ");
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        board->value[row][i] = strtoul(num_str, NULL, 10);
+        num_str = strtok(NULL, " ");
+    }
+}
+
+//
+
+BINGO_BOARD **read_cards(FILE *file, int *n_boards)
+{
+    char buf[BUFSIZ];
+    BINGO_BOARD **boards = calloc(BOARD_BUF_SIZ, sizeof(BINGO_BOARD *));
+    *n_boards = -1;
+    size_t row = 0;
+    while (fgets(buf, sizeof buf, file) != NULL)
+    {
+        if (buf[0] == '\n' || buf[0] == '\0')
+        {
+            row = 0;
+            (*n_boards)++;
+            boards[*n_boards] = new_bingo_board();
+            // printf("New board\n");
+        }
+        else
+        {
+            fill_bingo_board_row(boards[*n_boards], buf, row);
+            row++;
+        }
+    }
+    (*n_boards)++;
+    return boards;
+}
+
+unsigned int sum_unmarked_board(BINGO_BOARD *board)
+{
+    unsigned int sum = 0;
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            if (!board->state[i][j])
+                sum += board->value[i][j];
+        }
+    }
+    return sum;
+}
+
+bool mark_board(BINGO_BOARD *board, unsigned int n, unsigned int *answer)
+{
+    bool done = false;
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            if (board->value[i][j] == n && !board->state[i][j])
+            {
+                board->state[i][j] = true;
+                board->row_done[i]++;
+                board->column_done[j]++;
+                if (board->row_done[i] >= BOARD_SIZE || board->column_done[j] >= BOARD_SIZE)
+                {
+                    done = true;
+                }
+            }
+        }
+    }
+    if (done)
+    {
+        print_board(board);
+        *answer = n * sum_unmarked_board(board);
+        return true;
+    }
+    return false;
+}
+
+void mark_boards(BINGO_BOARD **boards, int n_boards, char *nums_str, unsigned int *answer)
+{
+    char *num_str = strtok(nums_str, ",");
+    while (num_str != NULL)
+    {
+        unsigned int number = strtoul(num_str, NULL, 10);
+        for (size_t i = 0; i < n_boards; i++)
+        {
+            if (mark_board(boards[i], number, answer))
+                return;
+        }
+        num_str = strtok(NULL, ",");
+    }
+}
+
+int main(int argc, char const *argv[])
+{
+    FILE *p_file = fopen("input", "r");
+    char buf[BUFSIZ];
+    fgets(buf, sizeof buf, p_file);
+    int n_boards;
+    BINGO_BOARD **boards = read_cards(p_file, &n_boards);
+    // for (size_t i = 0; i < n_boards; i++)
+    // {
+    //     printf("%d\n", i);
+    //     print_board(boards[i]);
+    // }
+
+    unsigned int answer;
+
+    mark_boards(boards, n_boards, buf, &answer);
+
+    printf("%d\n", answer);
+    exit(EXIT_SUCCESS);
+    return 0;
+}
diff --git a/4/4-2.c b/4/4-2.c
new file mode 100644
index 0000000..e327fab
--- /dev/null
+++ b/4/4-2.c
@@ -0,0 +1,172 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+#define BOARD_SIZE 5
+#define BOARD_BUF_SIZ 100
+
+typedef struct
+{
+    bool **state;
+    unsigned int **value;
+    unsigned int *column_done;
+    unsigned int *row_done;
+    bool won;
+} BINGO_BOARD;
+
+BINGO_BOARD *new_bingo_board()
+{
+    BINGO_BOARD *p_board = calloc(1, sizeof(BINGO_BOARD));
+    p_board->column_done = calloc(BOARD_SIZE, sizeof(unsigned int));
+    p_board->row_done = calloc(BOARD_SIZE, sizeof(unsigned int));
+    p_board->won = false;
+
+    p_board->state = calloc(BOARD_SIZE, sizeof(bool *));
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        p_board->state[i] = calloc(BOARD_SIZE, sizeof(bool));
+    }
+    p_board->value = calloc(BOARD_SIZE, sizeof(unsigned int *));
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        p_board->value[i] = calloc(BOARD_SIZE, sizeof(unsigned int));
+    }
+    return p_board;
+}
+
+void print_board(BINGO_BOARD *board)
+{
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            printf("%i(%i)\t", board->value[i][j], board->state[i][j]);
+        }
+        putchar('\n');
+    }
+}
+
+void *fill_bingo_board_row(BINGO_BOARD *board, char *line, char row)
+{
+    char *num_str = strtok(line, " ");
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        board->value[row][i] = strtoul(num_str, NULL, 10);
+        num_str = strtok(NULL, " ");
+    }
+}
+
+//
+
+BINGO_BOARD **read_cards(FILE *file, int *n_boards)
+{
+    char buf[BUFSIZ];
+    BINGO_BOARD **boards = calloc(BOARD_BUF_SIZ, sizeof(BINGO_BOARD *));
+    *n_boards = -1;
+    size_t row = 0;
+    while (fgets(buf, sizeof buf, file) != NULL)
+    {
+        if (buf[0] == '\n' || buf[0] == '\0')
+        {
+            row = 0;
+            (*n_boards)++;
+            boards[*n_boards] = new_bingo_board();
+            // printf("New board\n");
+        }
+        else
+        {
+            fill_bingo_board_row(boards[*n_boards], buf, row);
+            row++;
+        }
+    }
+    (*n_boards)++;
+    return boards;
+}
+
+unsigned int sum_unmarked_board(BINGO_BOARD *board)
+{
+    unsigned int sum = 0;
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            if (!board->state[i][j])
+                sum += board->value[i][j];
+        }
+    }
+    return sum;
+}
+
+unsigned int mark_board(BINGO_BOARD *board, unsigned int n)
+{
+    bool done = false;
+    for (size_t i = 0; i < BOARD_SIZE; i++)
+    {
+        for (size_t j = 0; j < BOARD_SIZE; j++)
+        {
+            if (board->value[i][j] == n && !board->state[i][j])
+            {
+                board->state[i][j] = true;
+                board->row_done[i]++;
+                board->column_done[j]++;
+                if (board->row_done[i] >= BOARD_SIZE || board->column_done[j] >= BOARD_SIZE)
+                {
+                    done = true;
+                }
+            }
+        }
+    }
+    if (done)
+    {
+        board->won = true;
+        // print_board(board);
+        return sum_unmarked_board(board);
+    }
+}
+
+void mark_boards(BINGO_BOARD **boards, int n_boards, char *nums_str, unsigned int *answer)
+{
+    char *num_str = strtok(nums_str, ",");
+    while (num_str != NULL)
+    {
+        unsigned int number = strtoul(num_str, NULL, 10);
+        unsigned int last_sum = 0, n_remaining_boards = 0;
+        for (size_t i = 0; i < n_boards; i++)
+        {
+            if (!boards[i]->won)
+            {
+                last_sum = mark_board(boards[i], number);
+                n_remaining_boards++;
+            }
+        }
+        if (n_remaining_boards == 1) //Imply last board
+        {
+            *answer = number * last_sum;
+        }
+
+        num_str = strtok(NULL, ",");
+    }
+}
+
+int main(int argc, char const *argv[])
+{
+    FILE *p_file = fopen("input", "r");
+    char buf[BUFSIZ];
+    fgets(buf, sizeof buf, p_file);
+    int n_boards;
+    BINGO_BOARD **boards = read_cards(p_file, &n_boards);
+    // for (size_t i = 0; i < n_boards; i++)
+    // {
+    //     printf("%d\n", i);
+    //     print_board(boards[i]);
+    // }
+
+    unsigned int answer;
+
+    mark_boards(boards, n_boards, buf, &answer);
+
+    printf("%d\n", answer);
+    exit(EXIT_SUCCESS);
+    return 0;
+}