This mission is an adaptation of the "Net" game (from Simon Tatham's Portable Puzzle Collection ). If you are lost or just want to play, the game is available here .

You have a rectangular grid with tiles you can only rotate, but it's a bit messy: tiles aren’t connected like they are supposed to be. You’ll have to put them in order by rotating each tile to reassemble the network .

The successful solution will be an entirely connected network with no closed loops.

There are four types of tiles:

• Dead ends
• Straight roads
• 90° turns
• T junctions

Tiles will be schematized by the directions to which they point ( N orth, W est, S outh, E ast), and more precisely with a string of directions (for example 'NE' if the tile is pointing to the Northeast, then it's a 90° turn).

Note that the order of directions in the string is meaningless (for example: 'NSE' and 'ENS' are the same) for input and output.

[['NW' , 'S'  , 'N'  , 'E'  , 'SE'],       [['SE' , 'W'  , 'S'  , 'E'  , 'SW'],
 ['NS' , 'W'  , 'NWE', 'NWE', 'SE'],        ['NS' , 'S'  , 'NSE', 'WSE', 'NW'],
 ['WSE', 'NSE', 'NWE', 'W'  , 'E' ],  ===\  ['NSE', 'NWE', 'NWS', 'N'  , 'S' ],
 ['WE' , 'WS' , 'WSE', 'SE' , 'WE'],  ===/  ['NS' , 'SE' , 'NWE', 'SW' , 'NS'],
 ['W'  , 'NE' , 'N'  , 'NW' , 'WS']]        ['N'  , 'NE' , 'W'  , 'NE' , 'NW']]

Input: A list of lists of strings.

Output: A list/tuple of lists/tuples of strings.

checkio([['NW' , 'S'  , 'N'  , 'E'  , 'SE'],
         ['NS' , 'W'  , 'NWE', 'NWE', 'SE'],
         ['WSE', 'NSE', 'NWE', 'W'  , 'E' ],
         ['WE' , 'WS' , 'WSE', 'SE' , 'WE'],
         ['W'  , 'NE' , 'N'  , 'NW' , 'WS']]) == [['SE' , 'W'  , 'S'  , 'E'  , 'SW'],
                                                  ['NS' , 'S'  , 'NSE', 'WSE', 'NW'],
                                                  ['NSE', 'NWE', 'NWS', 'N'  , 'S' ],
                                                  ['NS' , 'SE' , 'NWE', 'SW' , 'NS'],
                                                  ['N'  , 'NE' , 'W'  , 'NE' , 'NW']]

Preconditions:

• Given puzzles are solvable.
• 3 ≤ len(grid) ≤ 25, 3 ≤ len(grid[0]) ≤ 40.
• all(len(row) == len(grid[0]) for row in grid).