Game2048 | Python Fiddle

def game2048(grid, path):
    def rotated(grid):
        return [[grid[j][i] for j in range(4)] for i in range(4)]
    for direction in path:
        retGrid = []
        offset = -1 if direction in {'U', 'L'} else 1
        if direction in {'U', 'D'}:
            grid = rotated(grid) 
        for row in grid:
            retRow = []
            prevVal = None
            for val in filter(lambda x: x > 0, row[::-offset]):
                if prevVal:
                    if val == prevVal:
                        retRow = [2*val] + retRow
                        prevVal = None
                    else:
                        retRow = [prevVal] + retRow
                        prevVal = val
                else:
                    prevVal = val
            if prevVal:
                retRow = [prevVal] + retRow
            retRow = [0]*(4-len(retRow)) + retRow
            retGrid.append(retRow[::offset])
        grid = retGrid if direction in {'R', 'L'} else rotated(retGrid)
    return grid
    
print('%s', game2048([[0, 0, 0, 0],
          [0, 0, 2, 2],
          [0, 0, 2, 4],
          [2, 2, 4, 8]], 'RR'))

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