gistfile1.txt

#include <unistd.h>
#include <stdlib.h>

/*
 * board indexes
 *
 * 00 01 02 03
 * 04 05 06 07
 * 08 09 10 11
 * 12 13 14 15
*/

int view_indexes[][4] = {
    {0, 4, 8, 12},
    {1, 5, 9, 13},
    {2, 6, 10, 14},
    {3, 7, 11, 15},
    {12, 8, 4, 0},
    {13, 9, 5, 1},
    {14, 10, 6, 2},
    {15, 11, 7, 3},
    {0, 1, 2, 3},
    {4, 5, 6, 7},
    {8, 9, 10, 11},
    {12, 13, 14, 15},
    {3, 2, 1, 0},
    {7, 6, 5, 4},
    {11, 10, 9, 8},
    {15, 14, 13, 12}
};

void error(int code)
{
    write(1, "Error\n", 6);
    exit(code);
}

void parse_input(char *argv[], int views[16])
{
    int i;
    i = 1;
    while (i <= 16)
    {
        if (argv[i][0] < '1' || argv[i][0] > '4' || argv[i][1] != '\0')
        {
            error(100 + i);
        }
        views[i - 1] = (argv[i][0] - '0');
        i++;
    }
}

void print_board(int board[16])
{
    int row;
    row = 0;
    while (row < 4)
    {
        char c;
        int col;
        col = 0;
        while (col < 3)
        {
            c = '0' + board[4*row + col];
            write(1, &c, 1);
            write(1, " ", 1);
            col++;
        }
        c = '0' + board[4*row + col];
        write(1, &c, 1);
        write(1, "\n", 1);
        row++;
    }
}

void generate_board(long n, int board[16])
{
    int i;
    i = 0;
    while (i < 16)
    {
        int cell;
        cell = (n >> (30 - 2*i));
        cell &= 0x03;
        board[i] = (cell + 1);
        i++;
    }
}

void check_views(int board[16], int views[16])
{
    int view;
    view = 0;
    while (view < 16)
    {
        int cell_index_list_index;
        int visible_boxes;
        int higher_box;

        visible_boxes = 1;
        higher_box = board[view_indexes[view][0]];

        cell_index_list_index = 1;
        while (cell_index_list_index < 4)
        {
            int box_height = board[view_indexes[view][cell_index_list_index]];
            if (box_height > higher_box)
            {
                higher_box = box_height;
                visible_boxes++;
            }
            cell_index_list_index++;
        }
        if (visible_boxes != views[view])
        {
            break;
        }
        view++;
    }
    if (view == 16)
    {
        print_board(board);
        exit(0);
    }
}

void find_solution(int views[16])
{
    int board[16];
    long n;
    n = 0;
    while (n < 4294967296)
    {
        generate_board(n, board);
        check_views(board, views);
        n++;
    }
    error(2);
}

int main(int argc, char *argv[])
{
    if (argc != 17)
    {
        error(1);
    }
    int views[16];
    parse_input(argv, views);
    find_solution(views);

    return 0;
}