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Thread: Recursion problem
 10062010, 12:17 AM #1Member
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Recursion problem
I want to practice want I learned/didn't learn about recursion. I think I didn't learn much but I don't give up.
Here I want to calculate n*n + (n1)*(n1) + (n2)*(n2) + ... etc. using recursion.
Java Code:static long sum( int n ) { if( n == 0 ) return 0; //base case else { return (n*n) + sum(n1)*(n1); }
I thought the above code was correct in order to give me the desired result but it is not. When I input for example 5 result is 317.
I tracked variable n. It does go 54321012345 but the result is not 55.
Any ideas would be greatly appreciated.
 10062010, 12:50 AM #2Moderator
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return (n*n) + sum(n1)*(n1);
That line doesn't look right. It's saying "figure out n squared, then add that to the sum of the squares up to (n1) multiplied by (n1)". Why that last bit?
 10062010, 12:59 AM #3Member
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Last edited by luke; 10062010 at 01:05 AM.
 10062010, 01:32 AM #4Moderator
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I'm not sure if you've got this problem solved or not. (And I am deliberately loathe to provide code as this would defeat the whole purpose of the question.)
Here is your method rewritten with a more descriptive method name:
Java Code:static long sumOfSquaresUpTo(int n) { if(n == 0) return 0; //base case else { return (n*n) + sumOfSquaresUpTo(n1) *(n1); }
And I'm wondering if you can see why that last multiplication is wrong.
After all thesumofsquaresupto n is just n squared plus thesumofsquaresupto (n1).
 10062010, 03:02 AM #5Member
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 10062010, 06:14 AM #6Moderator
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Great. Glad to help.
 10062010, 06:35 AM #7Member
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