Generate a sequence using Recursion in Python [duplicate]

Question

I want to define a function as f(a,b) such that it generates a series as: 10,8,6,4,2,0,2,4,6,8,10 if a=10 and b=2 using Recursion.

def pattern(a,b):
    if a-b < 0:    
        print(a)
        return pattern(a+b,b)
        print(a)
    else:
        print(a)
        return pattern(a-b,b)

The result I get is

10
8
6
4
2
0
2
0
2
0
.....  infinity

... but this is wrong.

Albin Paul · Accepted Answer · 2019-10-18 05:55:48Z

2

You just need to use recursion

from __future__ import print_function
def psearch(a,b):
  if a > 0:
    print(a,end = ',')
    psearch(a - b,b)
    print(',',end="")
    print(a,end = "")
  else:
    print(a,end="")

psearch(12,5)
print()

OUTPUT

12,7,2,-3,2,7,12

edited Oct 18, 2019 at 5:55

answered Oct 18, 2019 at 4:57

Albin Paul

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6 Comments

Mir Muhammad Murtaza Over a year ago

2 issues: for example psearch(12,5) should give me 12,7,2,-3,2,7,12 but gives 12, 7, 2, 2, 7, 12 and towards the end 'None' is getting printed which should not be the case.

Albin Paul Over a year ago

@MirMuhammadMurtaza Nope, it gives the output you have said 12 7 2 -3 2 7 12. I just verified it now.

Albin Paul Over a year ago

@MirMuhammadMurtaza There is no None at the end produced in my program. It is because you are printing your function pattern() the function has None return value

Mir Muhammad Murtaza Over a year ago

12, 7, 2, -3, 2, 7, 12,. First point was my mistake. But there is a comma at the end when I use the argument in the print as end=', '. I need the commas but not at the end. Is there a way to achieve that ?

Albin Paul Over a year ago

@MirMuhammadMurtaza I have edited the answer to add commas instead of spaces.

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