Code Golf: Zigzag pattern scanning

Question

J, 13 15 characters

;<@|.`</.i.2$

Usage:

   ;<@|.`</.i.2$  3
0 1 3 6 4 2 5 7 8

   ;<@|.`</.i.2$  4
0 1 4 8 5 2 3 6 9 12 13 10 7 11 14 15

Explanation

(NB. is J's comment indicator)

;         NB. Link together...
<@|.`<    NB. ... 'take the reverse of' and 'take normally'
/.        NB. ... applied to alternating diagonals of...
i.        NB. ... successive integers starting at 0 and counting up to fill an array with dimensions of...
2$        NB. ... the input extended cyclically to a list of length two.

J, bonus, 13 characters

;<@|.`</.i.|.

Usage:

   ;<@|.`</.i.|. 3 4
0 1 3 6 4 2 5 7 9 10 8 11

   ;<@|.`</.i.|. 9 6
0 1 9 18 10 2 3 11 19 27 36 28 20 12 4 5 13 21 29 37 45 46 38 30 22 14 6 7 15 23 31 39 47 48 40 32 24 16 8 17 25 33 41 49 50 42 34 26 35 43 51 52 44 53

Python, 92, 95, 110, 111, 114, 120, 122, 162, 164 chars

N=input()
for a in sorted((p%N+p/N,(p%N,p/N)[(p%N-p/N)%2],p)for p in range(N*N)):print a[2],

Testing:

$ echo 3 | python ./code-golf.py 
0 1 3 6 4 2 5 7 8

$ echo 4 | python ./code-golf.py 
0 1 4 8 5 2 3 6 9 12 13 10 7 11 14 15

This solution easily generalizes for NxM boards: tweak the input processing and replace N*N with N*M:

N,M=map(int,raw_input().split())
for a in sorted((p%N+p/N,(p%N,p/N)[(p%N-p/N)%2],p)for p in range(N*M)):print a[2],

I suspect there's some easier/shorter way to read two numbers.

Testing:

$ echo 4 3 | python ./code-golf.py 
0 1 4 8 5 2 3 6 9 10 7 11

Ruby, 69 89 chars

n=gets.to_i
puts (0...n*n).sort_by{|p|[t=p%n+p/n,[p%n,p/n][t%2]]}*' '

89 chars

n=gets.to_i
puts (0...n*n).map{|p|[t=p%n+p/n,[p%n,p/n][t%2],p]}.sort.map{|i|i[2]}.join' '

Run

> zigzag.rb
3
0 1 3 6 4 2 5 7 8

> zigzag.rb
4
0 1 4 8 5 2 3 6 9 12 13 10 7 11 14 15

Credits to doublep for the sort method.

F#, 126 chars

let n=stdin.ReadLine()|>int
for i=0 to 2*n do for j in[id;List.rev].[i%2][0..i]do if i-j<n&&j<n then(i-j)*n+j|>printf"%d "

Examples:

$ echo 3 | fsi --exec Program.fsx
0 1 3 6 4 2 5 7 8

$ echo 4 | fsi --exec Program.fsx
0 1 4 8 5 2 3 6 9 12 13 10 7 11 14 15

Golfscript, 26/30 32/36 45 59 characters

Shortest non-J solution so far:

Updated sort (don't tell the others!) - 30 chars:

 ~:1.*,{..1/\1%+.2%.+(@*]}$' '* #solution 1
#~:\.*,{.\/1$\%+.1&@.~if]}$' '* #solution 2
#~\:1*,{..1/\1%+.2%.+(@*]}$' '* #(bonus)
#~\:\*,{.\/1$\%+.1&@.~if]}$' '* #(bonus)

---

Straight implementation - 36 chars:

 ~:@.*,{[.@%:|\@/:^+|^- 2%^|if]}$' '*
#~\:@*,{[.@%:|\@/:^+|^- 2%^|if]}$' '* #(bonus)

If you can provide output as "013642578" instead of "0 1 3 6 4 2 5 7 8", then you can remove the last 4 characters.

Credit to doublep for the sorting technique.

---

Explanation:

~\:@*        #read input, store first number into @, multiply the two
,            #put range(@^2) on the stack
{...}$       #sort array using the key in ...
" "*         #join array w/ spaces

and for the key:

[            #put into an array whatever is left on the stack until ]
.@%:|        #store @%n on the stack, also save it as |
\@/:^        #store @/n on the stack, also save it as ^
+            #add them together. this remains on the stack.
|^- 2%^|if   #if (| - ^) % 2 == 1, then put ^ on stack, else put | on stack.
]            #collect them into an array

MATLAB, 101/116 chars

Its basically a condensed version of the same answer given here, to be run directly on the command prompt:

N=input('');i=fliplr(spdiags(fliplr(reshape(1:N*N,N,N)')));i(:,1:2:end)=flipud(i(:,1:2:end));i(i~=0)'

and an extended one that read two values from the user:

S=str2num(input('','s'));i=fliplr(spdiags(fliplr(reshape(1:prod(S),S)')));i(:,1:2:end)=flipud(i(:,1:2:end));i(i~=0)'

Testing:

3
ans =
     1     2     4     7     5     3     6     8     9

and

4 3
ans =
     1     2     5     9     6     3     4     7    10    11     8    12