Generate a sequence using Recursion in Python

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 · 2019-10-18T05:55:48.787

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 '19 at 05:55

answered Oct 18 '19 at 04:57

Albin Paul

3,330
2
14
30

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. – Mir Muhammad Murtaza Oct 18 '19 at 05:13
@MirMuhammadMurtaza Nope, it gives the output you have said `12 7 2 -3 2 7 12`. I just verified it now. – Albin Paul Oct 18 '19 at 05:20
@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 – Albin Paul Oct 18 '19 at 05:21
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 ? – Mir Muhammad Murtaza Oct 18 '19 at 05:26
@MirMuhammadMurtaza I have edited the answer to add commas instead of spaces. – Albin Paul Oct 18 '19 at 05:56
Worked ! Thanks ! – Mir Muhammad Murtaza Oct 18 '19 at 06:13

Generate a sequence using Recursion in Python

1 Answers1