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Perfect Squares

 

Perfect Squares, Sample Excercise
EthanR

10 Sep, 2009 - 02:08 PM
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Assume there is a variable, h already associated with a positive integer value. Write the code necessary to compute the sum of the first h perfect squares, starting with 1 . (A perfect square is an integer like 9 , 16 , 25 , 36 that is equal to the square of another integer (in this case 3*3 , 4*4 , 5*5 , 6*6 respectively).) Associate the sum you compute with the variable q . For example, if h is 4 , you would assign 30 to q because the first 4 perfect squares (starting with 1 ) are: 1 , 4 , 9 , 16 and 30==1+4+9+16 .

For whatever reason I am having a difficult time solving this problem this is what I have but it is not correct.

q = sum(range(1,h+1,1)**2)
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shadhin

RE: Perfect Squares

10 Sep, 2009 - 02:49 PM
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Try this-
CODE

q=0
for i in range(1,h+1):
    q +=i**2
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reyno2ac

RE: Perfect Squares

10 Sep, 2009 - 04:59 PM
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I just made a list of all the perfect squares and then set q = to the sum of that list up to h.

CODE
perfect_square = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225]

q = sum(perfect_square[:h+1])


This post has been edited by reyno2ac: 10 Sep, 2009 - 05:00 PM
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Nallo

RE: Perfect Squares

11 Sep, 2009 - 09:51 AM
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Hello Ethan,
QUOTE(EthanR @ 10 Sep, 2009 - 02:08 PM) *
q = sum(range(1,h+1,1)**2)


This doesnt work, as range is a list (in Python 2.x, in Python 3.x it is a range object) and Python doesnt know what list ** 2 shall mean.
What you want is to put the elements of the list to power 2, so to write it in one line using list comprehension:

CODE
q = sum([i ** 2 for i in range(1, h + 1)])


or more elegantly using generator expression (Python 2.4(? not sure if it was 2.4) or later:
CODE
#in Python 2.x
q = sum(i ** 2 for i in xrange(1, h+1))
#in Python 3.x
q = sum(i ** 2 for i in range(1, h+1))

This is better than the above version, as the list is not stored in memory (for long lists that matters) before sum is called. Its elements are generated lazily, meaning only once they are needed.

This post has been edited by Nallo: 11 Sep, 2009 - 09:55 AM
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