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Geek, Programmer, FOSS Enthusiast, MS CS @USC. Loves Python / Django. Co-founder @ SMERGERS, Previously at Google, BlockBeacon, NI R&D

Tried writing some one liners for few problems in Projecteuler . had a good time writing them.. sharing the same..

I have used some functional programming techniques which make programming a lot of fun

map(function, sequence) : calls function(item) for each of the sequence's items and returns a list of the return values.

map ( int, [ '1', '2', '3' ] )

This is equivalent to :

[ int ( x ) for x in [ '1' , '2' , '3' ] ]

which is known as list comprehension.

which boils down to:

ints = [ ]
for element in [ '1', '2', '3' ]:
  ints.append ( int( element) )

We just applied an int function to all the elements of a list which contained numbers as strings.

reduce(function, sequence) : returns a single value constructed by calling the (binary) function on the first two items of the sequence, then on the result and the next item, and so on. For example, to compute the sum of the numbers 1 through 10:

reduce( sum , range(1, 11))

filter(function, sequence) returns a sequence consisting of those items from the sequence for which function(item) is true

def is_even(num):
  if num % 2 == 0:
    return True
  return False

filter( is_even , [ 1, 2, 3, 4] ) - > [ 2, 4]

Lambda functions : are used to create anonymous functions, i.e. functions which do not have a name. They are used as follows.

Previously we saw filtering of elements using the is_even method, the same filter using lambda function would look like this:

filter( lambda x: x% 2 == 0 , [ 1 , 2, 3 , 4] )

One liners for some of the problems


Note : Complexity of many of the solutions mentioned is bad.. This code was written to explore map, reduce, filter methods in python. If you think it can be improved ( by still maintaining the one line rule ), please leave a comment.


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