조금 허접하지만...그래도 for문 3개로 마무리..

#define MAX 7

    int data[MAX][MAX];
    int x,y,z;
    int m,n;

    m = MAX;
    n = 1;
    for(x=0; x<m; x++)
    {
        for(y=x; y<m; y++)
        {
            if(x%2) data[m-x/2-x%2][m-y-1+x/2] = n++;
            else    data[      x/2][    y-x/2] = n++;
        }
        n--;
        for(z=x; z<m; z++)
        {
            if(x%2) data[m-z+x/2][        x/2] = n++;
            else    data[  z-x/2][m-x/2-x%2-1] = n++;
        }
    }