leetcode 264. Ugly Number II

Posted 2020-09-27

leetcode 264. Ugly Number II

Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note that 1 is typically treated as an ugly number, and n does not exceed 1690.

 

三个list分别记录2的倍数，3的倍数，5的倍数，每次挑选出一个数以后就把他的2倍，3倍，5倍加入相应list

 

public class Solution {
    public int nthUglyNumber(int n) {
         if (n==0)return 0;
        int res=0;
        List<Integer> a = new LinkedList<Integer>();
        List<Integer> b = new LinkedList<Integer>();
        List<Integer> c = new LinkedList<Integer>();
        a.add(1);
        b.add(1);
        c.add(1);
        for (int i=0;i<n;i++){
            res=Math.min(a.get(0),Math.min(b.get(0),c.get(0)));
            if (res==a.get(0)){
                a.remove(0);
            }
            if (res==b.get(0)){
                b.remove(0);
            }

            if (res==c.get(0)){
                c.remove(0);
            }
            a.add(res*2);
            b.add(res*3);
            c.add(res*5);
        }
        return res;
    }
}