Ugly Number II

Problem

Return the n-th ugly number, where ugly numbers have only 2, 3 and 5 as prime factors and 1 is the first ugly number.

Maintain three pointers into the growing list for the next multiples of 2, 3 and 5, always appending the smallest next value and advancing every pointer that produced it. This keeps the list sorted and duplicate-free.

Hint

Advance every pointer that matches the appended value so 6 is generated once, not twice.

Test cases

case 1

in: [1]

expected: 1

case 2

in: [10]

expected: 12

case 3

in: [12]

expected: 16

case 4

in: [15]

expected: 24

case 5

in: [20]

expected: 36

Starter codePython

def nth_ugly_number(n):
    # Your code here
    pass

5 test cases · run your code against them in the editor