Ugly number doubt

#1


my solution is not correct
https://online.codingblocks.com/player/26926/content/8113/5286

#2

@bishtmanish786 Ugly numbers are those number whose prime factors are 2, 3 or 5.
The ugly-number sequence is 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, …
because every number can only be divided by 2, 3, 5, one way to look at the sequence is to split the sequence to three groups as below:
(1) 1×2, 2×2, 3×2, 4×2, 5×2, …
(2) 1×3, 2×3, 3×3, 4×3, 5×3, …
(3) 1×5, 2×5, 3×5, 4×5, 5×5, …
Then we use similar merge method as merge sort, to get every ugly number from the three subsequence. Every step we choose the smallest one, and move one step after.

So do something like this:

Begin
define array named uglyNum of size n
i2 := 0, i3 := 0, i5 := 0
next2mul := 2, next3mul := 3, next5Mul := 5
next := 1
ugluNum[0] := 1

for i := 1 to n, do
next := minimum of next2Mul, next3Mul and next5Mul
uglyNum[i] := next
if next = next2Mul, then
i2 := i2 + 1
next2mul := uglyNum[i2] x 2
if next = next3Mul, then
i3 := i3 + 1
next3mul := uglyNum[i3] x 3
if next = next5Mul, then
i5 := i5 + 1
next5mul := uglyNum[i5] x 5
done
return next
End

1 Like
#3

we have to print nth number of this sequence right ??
whats wrong with my code ? i printed nth number of this sequence …

#4

@bishtmanish786 Check for other test cases. According to your code 14 is also an ugly number but it is not.

#5

why 14 is not a ugly number .
14=2*7 have 2 prime factor and one of them is 2 so it should be ugly isn’t it??

#6

Ugly numbers are numbers whose only prime factors are 2, 3 or 5. Here 7 is also coming as a prime factor.

#7

ohh got it thanks
i will try it first

#8

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