An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.
Given an integer n, return true if n is an ugly number**.
Easy implementation, check if the number can be divided by 2 or 3 or 5, otherwise it's not an ugly number.
class Solution { public boolean isUgly(int n) { if (n <= 0) return false; while (n % 2 == 0) { n /= 2; } while (n % 3 == 0) { n /= 3; } while (n % 5 == 0) { n /= 5; } return n == 1; } }
An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.
Given an integer n, return the nth ugly number.
This question is to generate the ugly number. Start from num1, and each time it pick the smallest number from current number multiple 2 or 3 or 5.
class Solution { public int nthUglyNumber(int n) { int index2 = 0, index3 = 0, index5 = 0; int[] nums = new int[n]; nums[0] = 1; for (int i = 1; i < n; i++) { int num2 = nums[index2] * 2; int num3 = nums[index3] * 3; int num5 = nums[index5] * 5; nums[i] = Math.min(num2, Math.min(num3, num5)); if (nums[i] == num2) index2++; if (nums[i] == num3) index3++; if (nums[i] == num5) index5++; } return nums[n - 1]; } }