Looping in a spiral

Question

A friend was in need of an algorithm that would let him loop through the elements of an NxM matrix (N and M are odd). I came up with a solution, but I wanted to see if my fe

Answer 1

Here is my attempt for simple C solution. First print the outer spiral and move one block inside..and repeat.

#define ROWS        5
#define COLS        5
//int A[ROWS][COLS] = { {1, 2, 3, 4}, {5, 6, 7, 8}, {11, 12, 13, 14}, {15, 16, 17, 18} };
//int A[ROWS][COLS] = { {1, 2, 3}, {6, 7, 8}, { 12, 13, 14} };
//int A[ROWS][COLS] = { {1, 2}, {3, 4}};

int A[ROWS][COLS] = { {1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}, {11, 12, 13, 14, 15} , {16, 17, 18, 19, 20}, {21, 22, 23, 24, 25} };


void print_spiral(int rows, int cols)
{
    int row = 0;
    int offset = 0;

    while (offset < (ROWS - 1)) {
        /* print one outer loop at a time. */
        for (int col = offset; col <= cols; col++) {
            printf("%d ", A[offset][col]);
        }

        for (row = offset + 1; row <= rows; row++) {
            printf("%d ", A[row][cols]);
        }

        for (int col = cols - 1; col >= offset; col--) {
            printf("%d ", A[rows][col]);
        }

        for (row = rows - 1; row >= offset + 1; row--) {
            printf("%d ", A[row][offset]);
        }

       /* Move one block inside */
        offset++;
        rows--;
        cols--;
    }
    printf("\n");
}

int _tmain(int argc, _TCHAR* argv[])
{
    print_spiral(ROWS-1, COLS-1);
    return 0;
}