Write a program or function that takes in a positive integer N and a grid of decimal digits (0 to 9) with width W and height H (which are also positive integers). You can assume that N will be less than or equal to the larger of W and H.

Print or return the largest contiguous N digit number that appears horizontally or vertically in the grid, written in normal reading order or in reverse.

  • Diagonal lines of digits are not considered.
  • The grid does not wrap around, i.e. it does not have periodic boundary conditions.

For example, the 3×3 grid


would have 9 as the output for N = 1, 94 as the output for N = 2, and 940 as the output for N = 3.

The 4×3 grid


would have 8 as the output for N = 1, 86 for N = 2, 854 for N = 3, and 7423 for N = 4.

The 3×3 grid


would have output 1 for N = 1, and 10 for N = 2 and N = 3 (010 is also valid for N = 3).

The 1×1 grid


would have output 0 for N = 1.

You can take the input in any convenient reasonable format. e.g. the grid could be a newline separated string of digits, or a multidimensional array, or a list of lists of digits, etc. Leading zeros are allowed in the output if they were part of the grid.

This is , so the shortest code in bytes wins, but I'll also award brownie points (i.e. more likely upvotes) for answers that can show that their algorithm is computationally efficient.

  • 1
    \$\begingroup\$ Are we allowed to print any leading zeroes? \$\endgroup\$ – PurkkaKoodari Nov 6 '15 at 7:22
  • \$\begingroup\$ @Pietu1998 "Leading zeros are allowed in the output if they were part of the grid." \$\endgroup\$ – Calvin's Hobbies Nov 6 '15 at 15:12

Pyth, 22 19 bytes

3 bytes thanks to Jakube.


Try it online.

If we are allowed to print leading zeroes, the code is 18 bytes:

  • \$\begingroup\$ Converting a string with leading zeros to an integer can be accomplished with s. \$\endgroup\$ – Jakube Nov 7 '15 at 14:15

CJam, 39 36 35 34 bytes


Just quickly, before @Dennis wakes up :P

Try it online.


The basic algorithm is to take all four rotations of the grid and split each row into chunks of length N (or the row length, whichever's smaller). Then convert the chunks to ints and take the largest.

qN/             Split input by newlines, giving an array of lines
)i\             Drop N from the array and put at bottom
[        ]      Wrap in array...
 {    }4*         Perform 4 times...
  zW%_              Rotate grid anticlockwise and push a copy
                Note that this gives an array of 5 grids [CCW1 CCW2 CCW3 CCW4 CCW4]
ff{         }   For each grid row, mapping with N as an extra parameter...
   _,             Push length of row
     @e<          Take min with N
        ew        Split into chunks
          :i      Convert to ints
e_              Flatten that array
:e>             Take cumulative max
  • \$\begingroup\$ Out of curiosity, does few do anything special, or is it three separate commands? \$\endgroup\$ – ETHproductions Nov 6 '15 at 4:37
  • 3
    \$\begingroup\$ @ETHproductions It's actually the operator ew applied using f, or "map with extra parameter". For example, ["abcd" "efgh"] 2 few results in [["ab" "bc" "cd"] ["ef" "fg" "gh"]]. \$\endgroup\$ – Sp3000 Nov 6 '15 at 4:39
  • \$\begingroup\$ Gotcha :) That's an interesting coincidence, though. \$\endgroup\$ – ETHproductions Nov 6 '15 at 4:54
  • \$\begingroup\$ Only issue is that, when @Dennis wakes up, everybody else loses anyway. ;) \$\endgroup\$ – kirbyfan64sos Nov 6 '15 at 13:35


Not a final answer yet but it probably will work like this:

blsq ) "7423\n1531\n6810"ln)XXJ)\[jtp)\[_+J)<-_+{3.+ti}m[>]
blsq ) "7423\n1531\n6810"ln)XXJ)\[jtp)\[_+J)<-_+{4.+ti}m[>]

How is N and the grid given exactly?

  • \$\begingroup\$ One should typically wait to post an answer until it's works. Any questions for the OP should be given as comments on the post. \$\endgroup\$ – Alex A. Nov 6 '15 at 20:54
  • \$\begingroup\$ The code actually works. \$\endgroup\$ – mroman Nov 7 '15 at 8:48

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