merge.py

#!/usr/bin/env python2
import doctest


def shift_zeros(line):
    no_zeros = [each for each in line if each != 0]   # make a list with no zeroes
    return no_zeros + ([0] * (len(line) - len(no_zeros)))   # return the list with the zeroes added at the end


def merge(line):
    """
    (list) -> list
    Function that merges a single row or column in 2048.
    >>> merge([1,1,0,1])
    [2, 1, 0, 0]

    >>> merge([1,2,2,1])
    [1, 4, 1, 0]

    >>> merge([1,0,1,0,1,1,0,0,0,0,0,1])
    [2, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0]

    >>> merge([1,2,1,2,0])
    [1, 2, 1, 2, 0]
    """
    line = shift_zeros(line)   # shift all the zeroes to the right
    for idx in range(len(line) - 2):  # skip the last idx (would cause an error on the next line)
        if line[idx] == line[idx + 1]:   # check if neighbouring idxs are of the same value
            line[idx], line[idx + 1] = line[idx] * 2, 0    # multiply the first idx by 2, and the neighbouring make a 0
    return shift_zeros(line)   # return the list with zeroes shifted out

if __name__ == '__main__':
    doctest.testmod()
    print merge([1, 0, 1, 0, 1, 1, 0, 0, 1])
    print merge([1, 2, 1, 3, 0])
    raw_input('Press Enter')