Another Easy Beginner Question


D

danielj

There is a song that goes like this:

On the first day of Christmas, my true love sent to me a partridge
in a pear tree.
On the second day of Christmas, my true love sent to me two turtle
doves and a partridge in a pear tree.
...

If this goes on for the 12 days of Christmas. How many presents will
your true love send you over Christmas?
<strong>(Hint: You will need a loop inside another). </strong>

I don't think you need a loop inside a loop.... Here is what I did:

day = 0
gifts = 0

12.times do
day = day + 1
gifts = gifts + day
end

print gifts

Does anyone know how you would do it with a <em>loop inside a loop</
em>?
 
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S

Sammy Larbi

I'm not sure why you'd want to, but I suppose you could do something like:

gifts=0
(1..12).each do |i|
(1..i).each { |j| gifts += 1 }
end
puts gifts

danielj wrote, On 6/18/2007 11:50 AM:
 
D

danielj

I just wanted to do the challenge correctly...

Although, maybe I shouldn't be doing a tutorial with that kind of lame
challenge...
 
A

Alex LeDonne

There is a song that goes like this:

On the first day of Christmas, my true love sent to me a partridge
in a pear tree.
On the second day of Christmas, my true love sent to me two turtle
doves and a partridge in a pear tree.
...

If this goes on for the 12 days of Christmas. How many presents will
your true love send you over Christmas?
<strong>(Hint: You will need a loop inside another). </strong>

I don't think you need a loop inside a loop.... Here is what I did:

day = 0
gifts = 0

12.times do
day = day + 1
gifts = gifts + day
end

print gifts

Does anyone know how you would do it with a <em>loop inside a loop</
em>?


Note that your program does not solve the problem (which is easy to
misinterpret). To clarify the problem:

On day 1, you get 1 gift.
On day 2, you get 3 gifts, not two (two doves AND one bird/tree combo).
On day 3, you get 6 gifts - 3 hens, 2 doves, one more pear tree
w/attendant partridge.
and so on... until
On day 11 you get 66 gifts, and
On day 12 you get 78 gifts.


Do you see how a loop within a loop may be helpful?

Good luck!

-A
 
S

Stephen Ball

Remember to count each gift for each day (on the second day you get
another bird in a tree, on the third day you get two more doves and
another bird in a tree, etc.)

day = 0
gifts_for_the_day = 0
total_gifts = 0

12.times do
day += 1
gifts_for_the_day += day
total_gifts += gifts_for_the_day
puts "Day: #{day}, Gifts for Day: #{gifts_for_the_day}, Total gifts:
#{total_gifts}"
end

-- Stephen
 
D

Daniel Kempkens

Alex said:
Note that your program does not solve the problem (which is easy to
misinterpret). To clarify the problem:

On day 1, you get 1 gift.
On day 2, you get 3 gifts, not two (two doves AND one bird/tree combo).
On day 3, you get 6 gifts - 3 hens, 2 doves, one more pear tree
w/attendant partridge.
and so on... until
On day 11 you get 66 gifts, and
On day 12 you get 78 gifts.


Do you see how a loop within a loop may be helpful?

Good luck!

-A
Well, I solved this for fun, my code looks like this:

def gift_counter(max = 12)
gifts = 0
1.upto(max) do |day|
gifts += day # I guess 'day' is a bad var-name here :D
puts "Day: {#day}, Gifts: #{gifts}"
end
end

It works quite good, so why does this Quiz-Site suggest to use two
loops? Am I getting something of this quiz wrong?
 
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A

Alex LeDonne

Well, I solved this for fun, my code looks like this:

def gift_counter(max = 12)
gifts = 0
1.upto(max) do |day|
gifts += day # I guess 'day' is a bad var-name here :D
puts "Day: {#day}, Gifts: #{gifts}"
end
end

It works quite good, so why does this Quiz-Site suggest to use two
loops? Am I getting something of this quiz wrong?

Well, the original question is:
What is the total number of gifts given over the 12 days?

The gift_counter is good for the number by-the-day, but the question
is asking for a gift_totaler.

-A
 
P

Phrogz

Well, I solved this for fun, my code looks like this:

def gift_counter(max = 12)
gifts = 0
1.upto(max) do |day|
gifts += day # I guess 'day' is a bad var-name here :D
puts "Day: {#day}, Gifts: #{gifts}"
end
end

It works quite good, so why does this Quiz-Site suggest to use two
loops? Am I getting something of this quiz wrong?

Does it work? It tells you how many gifts you GET on each day, but
does not tell you how many gifts you HAVE when the day is done.

On day 1 you get 1 gift, resulting in 1 gift owned by you.
On day 2 you get 3 gifts, resulting in 4 gifts owned by you.
On day 3 you get 6 gifts, resulting in 10 gifts owned by you.
 
S

Sammy Larbi

I originally thought it boiled down to

1+2+...+11+12=78

But now that I think about it again, I'm pretty sure I was wrong. The
correct sequence is:

(1) + (1+2) + (1+2+3) + ... + (1+2+...+11+12)

Which I think makes you right.

Sam


Matt Filizzi wrote, On 6/18/2007 12:19 PM:
 
D

Daniel Kempkens

Phrogz said:
Does it work? It tells you how many gifts you GET on each day, but
does not tell you how many gifts you HAVE when the day is done.

On day 1 you get 1 gift, resulting in 1 gift owned by you.
On day 2 you get 3 gifts, resulting in 4 gifts owned by you.
On day 3 you get 6 gifts, resulting in 10 gifts owned by you.
I think I missed the total-part of the quiz ;) But implementing a
total-counter wouldn't be much difficult.
 
D

danielj

I see...

Thanks all...

It was really helpful to see the problem thought about many different
ways
 
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G

Gregory Brown

I think I missed the total-part of the quiz ;) But implementing a
total-counter wouldn't be much difficult.

Wouldn't it be:

def fact(n); n > 1 ? n + fact(n-1) : 1; end
puts (1..12).inject(0) { |s,r| s + fact(r) }
 
E

Eric I.

Wouldn't it be:

def fact(n); n > 1 ? n + fact(n-1) : 1; end
puts (1..12).inject(0) { |s,r| s + fact(r) }

That certainly works, although I'm personally uncomfortable with the
name of your recursive method; "fact" seems to imply factorial, which
this is not.

If you like inject, how about a pair of 'em:

puts (1..12).inject(0) { |sum, day|
sum + (1..day).inject { |day_sum, gifts| day_sum + gifts }
}

Eric
 
M

Morton Goldberg

Wouldn't it be this...

gifts = 0
(1..12).each do |x|
(1..x).each do { |y| gifts += y } ^^
end
puts gifts

Not quite. It should be:

<code>
gifts = 0
(1..12).each do |x|
(1..x).each { |y| gifts += y }
end
gifts # => 364
</code>

But this problem has a nice closed-form solution:

<code>
def gifts(days)
days * (days +1) * (days + 2) / 6
end
gifts(12) # => 364
</code>

Regards, Morton
 
G

Gregory Brown

That certainly works, although I'm personally uncomfortable with the
name of your recursive method; "fact" seems to imply factorial, which
this is not.

Dur. You're right. 12! = 12*11*10*..

/me is a math major, too.
If you like inject, how about a pair of 'em:

puts (1..12).inject(0) { |sum, day|
sum + (1..day).inject { |day_sum, gifts| day_sum + gifts }
}

yup, that looks pretty good.
 
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D

Drew Olson

Eric said:
puts (1..12).inject(0) { |sum, day|
sum + (1..day).inject { |day_sum, gifts| day_sum + gifts }
}

I'd do it as shown below, but it's probably not covered by the point in
the book you're currently at:

irb(main):001:0> class Integer
irb(main):002:1> def int_sum
irb(main):003:2> (1..self).inject(0){|sum,n|sum+n}
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> puts (1..12).inject(0){|sum,n|sum+n.int_sum}
364
=> nil
 
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