[Tutor] Beginner's question

[Peter O'Doherty]

On 11/22/2012 03:17 PM, Walter Prins wrote:
> Hi Peter,
>
>
> On 22 November 2012 12:55, Peter O'Doherty <mail at peterodoherty.net 
> <mailto:mail at peterodoherty.net>> wrote:
>
>     Hi list,
>     Firstly, apologies for the low-level nature of this question -
>     it's really quite basic but I don't seem to be able to solve it.
>
>     I need to write a program that examines 3 variables x, y, z, and
>     prints the largest odd number. I've tried all sorts of variations
>     and this is the current version:
>
>     x, y, z = 26, 15, 20
>
>     if x > y and x > z and x%2 != 0:
>         print 'x is largest and odd'
>     elif y > x and y > z and y%2 != 0:
>         print 'y is largest and odd'
>     elif z > x and z > y and z%2 != 0:
>         print 'z is largest and odd'
>     else:
>         print 'no odd'
>
>
> The key logical mistake you make is that by your current logic the 
> *smallest* number can never be the largest odd number, which is 
> obviously false as in your example.
>
> Break the problem down (divide and conquer).  Suppose I gave you only 
> 2 numbers, and you had to say which of the 2 numbers were the largest 
> odd, what would be the possible outcomes and what would the the 
> solution be?  (Hint, both can be odd, only x can be odd, only y can be 
> odd, or neither can be odd.)   Once you have that answer, then repeat 
> the exact same solution for the first 2 numbers and apply to the 
> answer from x&y and and the remaining z.  The result from that is 
> tells you the largest odd number from all 3. (Aside, your question 
> states to print the largest odd number, which I interpret to mean the 
> value, not the name of the variable holding the value.  )
>
> Walter

Thanks Walter.

This code appears to work although it's very cumbersome. Is there a 
better way to do it?

x, y, z = 6, 23, 16

if x%2 != 0 and y%2 !=0:
     if x > y:
         ans = x
     else:
         ans = y
elif x%2 !=0 and y%2 == 0:
     ans = x
else:
     ans = y

if ans%2 != 0 and z%2 !=0:
     if ans > z:
         ans = ans
     else:
         ans = z
elif ans%2 !=0 and z%2 == 0:
     ans = ans
else:
     ans = z
print str(ans) + ' is largest odd'

Regards,
Peter


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//=============================
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-> http://www.peterodoherty.net
-> mail at peterodoherty.net
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