integer n = 5
string fmt = sprintf("%%%dd",length(sprintf("%d",n*n-1)))
sequence m = repeat(repeat("??",n),n)
integer x = 1, y = 1
for d=0 to n*n-1 do
    m[y][x] = sprintf(fmt,d)
    if mod(x+y,2) then
        {x,y} = iff(y<n?{x-(x>1),y+1}:{x+1,y})
    else
        {x,y} = iff(x<n?{x+1,y-(y>1)}:{x,y+1})
    end if
end for

for i=1 to n do
    m[i] = join(m[i])
end for
puts(1,join(m,"\n"))