This week's book giveaway is in the Java 8 forum.
We're giving away four copies of Java 8 in Action and have Raoul-Gabriel Urma, Mario Fusco, and Alan Mycroft on-line!
See this thread for details.
The moose likes Programming Diversions and the fly likes [Easy] Find 9 Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login


Win a copy of Java 8 in Action this week in the Java 8 forum!
JavaRanch » Java Forums » Other » Programming Diversions
Bookmark "[Easy] Find 9" Watch "[Easy] Find 9" New topic
Author

[Easy] Find 9

Michael Morris
Ranch Hand

Joined: Jan 30, 2002
Posts: 3451
Excluding 1-9, find the smallest consecutive group of 9 positive integers such that the first ends in 1 and the last ends in 9 and the result of dividing each by its last digit yields no remainder. For example:
512/2 has no remainder.
123/3 has no remainder.
637/7 has no remainder.


Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction. - Ernst F. Schumacher
Eric Pascarello
author
Rancher

Joined: Nov 08, 2001
Posts: 15376
    
    6
Wrote this in < minute....lol
http://www10.brinkster.com/A1ien51/game/Solver9.htm
I was expecting the number to be in the 1000 range, but was surprised to see it was higher.
Eric
Michael Morris
Ranch Hand

Joined: Jan 30, 2002
Posts: 3451
Wrote this in < minute....lol
So what you want a cookie? :roll: I said it was easy.
Eric Pascarello
author
Rancher

Joined: Nov 08, 2001
Posts: 15376
    
    6
Originally posted by Michael Morris:
So what you want a cookie? :roll: I said it was easy.

Peanut Butter Please
Jim Yingst
Wanderer
Sheriff

Joined: Jan 30, 2000
Posts: 18671
Wrote this in < minute....lol
That's about how long it takes in a real programming language too. Except we don't have to wait several more seconds afterwards for the result.

There are probably ways to reduce the number of computations more (aside from eliminating checks for 1, 2, 5, which are trivial) but given how quickly the answer is found anyway, it hardly seems necessary.
[ June 01, 2003: Message edited by: Jim Yingst ]

"I'm not back." - Bill Harding, Twister
Jessica Sant
Sheriff

Joined: Oct 17, 2001
Posts: 4313

Mine's a bit different than Jim's:

[ June 01, 2003: Message edited by: Jessica Sant ]

- Jess
Blog:KnitClimbJava | Twitter: jsant | Ravelry: wingedsheep
Eric Pascarello
author
Rancher

Joined: Nov 08, 2001
Posts: 15376
    
    6
LOL, I could speed it up if I wanted too....lol
Michael Morris
Ranch Hand

Joined: Jan 30, 2002
Posts: 3451
Well since it's show and tell
Jim Yingst
Wanderer
Sheriff

Joined: Jan 30, 2000
Posts: 18671
For the record, mine was just intended as a quick and dirty solution; once I saw how quickly the solution popped up, any further refactoring seemed pointless. Though looking at other solution, I did like Michael's use of i > 0 to terminate the loop in case no solution was found otherwise. I had started to put in i <= (Integer.MAX_VALUE) - 10) but first I decided to run the program anyway; turned out it didn't matter. But using i > 0 is an elegant check I'll remember next time.
Roy Tock
Ranch Hand

Joined: Jul 16, 2001
Posts: 83
Mathematical solution:
This problem is equivalent to finding the smallest positive integer (divisible by 10) that is (also) divisible by 2, 3, 4, 5, 6, 7, 8, and 9. Since the number is divisible by 2 and 5, it's trivially divisible by 10.
To find the LCM of a series of numbers, find their prime representations, choose the max exponent of each prime factor, and multiply together.
9 = 3^2
8 = 2^3
7 = 7
6 = 2 * 3
5 = 5
4 = 2^2
3 = 3
2 = 2
The LCM is 7 * 5 * 3^2 * 2^3, or 2520, so the nine integers we seek are the nine following 2520.
 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: [Easy] Find 9
 
Similar Threads
[Medium] Find 9 with a twist
Convert Decimal to Binary No.
conversion of binary and hex to decimal and about left/right shift
Finding recurring cycle in a decimal.
converting numbers to roman numerals