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sumDigits  challenge

Posted on 2016-09-09
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Last Modified: 2016-09-11
Hi,

http://codingbat.com/prob/p163932

I am working on above challenge
Given a non-negative int n, return the sum of its digits recursively (no loops). Note that mod (%) by 10 yields the rightmost digit (126 % 10 is 6), while divide (/) by 10 removes the rightmost digit (126 / 10 is 12).

sumDigits(126) → 9
sumDigits(49) → 13
sumDigits(12) → 3

i was not sure how to find the sum of digits recursively without loop which i worked earlier. please advise
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Question by:gudii9
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7 Comments
 
LVL 27

Expert Comment

by:d-glitch
ID: 41792111
Do you remember how to break up an integer into the LAST digit and the REST using % and / .

Recursion works by letting a function call itself multiple times, each time with a smaller or simpler argument.

The pseudo code would be something like:
function sumDigits( n)
sum = 0
if arg = 0 
     return sum
else
     sum = sum + LAST( arg) + sumDigits( REST( arg))

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RECURSION is probably the single most important and elegant topic in computer science.
You should really read up on it if you don't understand the concept.  Challenges are not going to be enough.
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Author Comment

by:gudii9
ID: 41792185
Do you remember how to break up an integer into the LAST digit and the REST using % and / .
yes
RECURSION is probably the single most important and elegant topic in computer science.
You should really read up on it if you don't understand the concept.  Challenges are not going to be enough.
where should i read up on it? Any best material,book, site?
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LVL 27

Accepted Solution

by:
d-glitch earned 250 total points
ID: 41792669
Here are a couple of references:
     http://introcs.cs.princeton.edu/java/23recursion/
     http://arxiv.org/pdf/cs/9301113


My pseudo code needs some mods:
function sumDigits( n)
if n = 1   
     return 1
else   
     return  LAST + sumDigits( REST)

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LVL 27

Assisted Solution

by:rrz
rrz earned 250 total points
ID: 41793107
My pseudo code is a little different from d-glitch
if input is 0 then return 0
if not then return last + sumDigits(rest)
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LVL 7

Author Comment

by:gudii9
ID: 41793534
I will try
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LVL 7

Author Comment

by:gudii9
ID: 41793651
public int sumDigits(int n) {
  if (n < 10) 
{return n;
}
  return (n % 10) + sumDigits(n/10);
}

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above passes all test. any improvements or alternate approaches?
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LVL 27

Expert Comment

by:rrz
ID: 41793722
 if (n < 10)
{return n;
Brilliant! I like your base case much better.
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