Project Euler Python

Question

I am working on the Project Euler problems. I am on Problem 1 and for some reason I am getting the wrong answer for it. I don't know if its my math logic that's the problem or if the logic for the code is wrong. Here's the code:

def getSumMult3_5(n):
    count = 0
    i = 0
    i_1 = 0
    while i*5 < n:
        count += i*5
        i += 1
    while i_1*3 < n:
        count += i_1*3
        i_1 += 1
    return count

print getSumMult3_5(1000)

It's returning that

count = 266333

but that is not the correct answer. Count should equal 233168. Can anybody help me figure out why it's doing this?

Thanks!

AGreenman · Accepted Answer · 2015-02-09 19:44:15Z

2

You're double counting numbers that are multiples of both 5 and 3, such as 15.

answered Feb 9, 2015 at 19:44

AGreenman

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1 Comment

Robbie Over a year ago

Oh wow I'm stupid. I didn't read the question carefully. It's multiples of 3 OR 5! Thanks so much

anonymouskoala3307 · Accepted Answer · 2019-06-30 21:55:34Z

You are double counting multiples of 15. You can solve this by introducing a third while statement to decrease the count by 1 for each multiple of 15.

I suggest using an if/else statement:

def getSumMult3_5(n):
  s = 0
  for i in range(1, n+1):
    if i%3==0:
      s+=i
    elif i%5==0:
      s+=i
  return s

print getSumMult3_5(1000)

This is because that if the number is a multiple of 3, it does not check whether it is a multiple of 5; if it is not a multiple of 3, it checks whether it is a multiple of 5.

I also recommend using s as a variable name because it represents sum, which can't be used as it is a keyword. Count seems to refer to the number of times something occurs.

By only using one variable, and using an if/else statement, execution time will be less and it will be less confusing to read.

Good luck!

DavidW · Accepted Answer · 2020-06-24 20:08:34Z

0

Here's my code:

running_sum = 0





for i in range(1,1000):
    if i % 3 == 0:
      running_sum+=(i) 
      
    elif i % 5 == 0:
      running_sum+=(i)
print running_sum

You're double-counting numbers like 15 that are multiples of both

edited Jun 24, 2020 at 20:08

DavidW

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answered Jun 23, 2020 at 20:25

Anirudh

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