# Description

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.

The original problem is here.

The original code is here.

# My Solution

I solve this problem in C++, as below:

``````/*
*Ugly Number2
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
*/
#include<iostream>
#include<vector>
#include<stdlib.h>
using namespace std;

class Solution {
public:
int nthUglyNumber(int n) {
if(n <= 0)
return -1;
if(n == 1)
return 1;
int n1 = 0, n2 = 0, n3 = 0;
vector<int> L1, L2, L3;
L1.push_back(2);
L2.push_back(3);
L3.push_back(5);
int num = 1;
for(int count=2;count<=n;count++){
int minNum=min(L1[n1],min(L2[n2],L3[n3]));

L1.push_back(minNum * 2);
L2.push_back(minNum * 3);
L3.push_back(minNum * 5);

if(L1[n1] == minNum)
n1 ++;
if(L2[n2] == minNum)
n2 ++;
if(L3[n3] == minNum)
n3 ++;
num = minNum;
//cout<<num<<endl;
}
return num;
}
};

int main()
{
Solution s;
int num = s.nthUglyNumber(12);
cout<<"num="<<num<<endl;
system("pause");
return 0;
}
``````

# Note

Three lists were used to save the ugly numbers. From 1-th to n-th ugly number, select the minimum of the three lists.