Task

Produce a zig-zag array.



A   zig-zag   array is a square arrangement of the first   N2   natural numbers,   where the

numbers increase sequentially as you zig-zag along the array's   anti-diagonals.

For a graphical representation, see   JPG zigzag   (JPG uses such arrays to encode images).



For example, given   5,   produce this array:

 0  1  5  6 14
 2  4  7 13 15
 3  8 12 16 21
 9 11 17 20 22
10 18 19 23 24



Related tasks

   Spiral matrix
   Identity matrix
   Ulam spiral (for primes)


See also

   Wiktionary entry:   anti-diagonals


public static int[,] ZigZag(int n)
{
    int[,] result = new int[n, n];
    int i = 0, j = 0;
    int d = -1; // -1 for top-right move, +1 for bottom-left move
    int start = 0, end = n * n - 1;
    do
    {
        result[i, j] = start++;
        result[n - i - 1, n - j - 1] = end--;
 
        i += d; j -= d;
        if (i < 0)
        {
            i++; d = -d; // top reached, reverse
        }
        else if (j < 0)
        {
            j++; d = -d; // left reached, reverse
        }
    } while (start < end);
    if (start == end)
        result[i, j] = start;
    return result;
}