丑数

Version 1

/*
	丑数
*/

#include <iostream>
using namespace std;

int divide(int n, int m);
int isUgly(int n);

int main()
{
	int n = 1;
	int account = 0;
	int num = 100;

	while (1)
	{
		if (isUgly(n))
		{
			cout<<n<<endl;
			account++;
		}
		
		if (account == num)
		{
			break;
		}

		n++;
	}
	system("pause");
	return 0;
}

int divide(int n, int m)
{
	while (n % m == 0)
	{
		n = n / m;
	}

	return n;
}

int isUgly(int n)
{
	n = divide(n, 2);
	n = divide(n, 3);
	n = divide(n, 5);

	return (n == 1) ? 1 : 0;
}

Version 2: Dynamic Programming : Bottom Up (Tabulation)

#include <iostream>
using namespace std;

#define bool int
 
unsigned int min(unsigned int a, unsigned int b);
unsigned int Minimum(unsigned int a, unsigned int b, unsigned int c);
unsigned int getNthUglyNo(unsigned int n);
 
int main()
{
	unsigned int num = 150;
    unsigned int no = getNthUglyNo(num);
	cout<<"The "<<num<<" Ugly num is: "<<no<<endl;
    getchar();

    return 0;
}

/* Function to get the nth ugly number*/
unsigned int getNthUglyNo(unsigned int n)
{
    unsigned int *ugly = new unsigned int [n];
    unsigned int i2 = 0, i3 = 0, i5 = 0;
    unsigned int next_multiple_of_2 = 2;
    unsigned int next_multiple_of_3 = 3;
    unsigned int next_multiple_of_5 = 5;
    unsigned int next_ugly_no = 1;

    ugly[0] = 1;
 
    for(unsigned int i=1; i<n; i++)
    {
       next_ugly_no = Minimum(next_multiple_of_2, next_multiple_of_3, next_multiple_of_5);
       
	   ugly[i] = next_ugly_no;                    
       
	   if(next_ugly_no == next_multiple_of_2)
       {
           i2 = i2 + 1;       
           next_multiple_of_2 = ugly[i2] * 2;
       }

       if(next_ugly_no == next_multiple_of_3)
       {
           i3 = i3 + 1;
           next_multiple_of_3 = ugly[i3] * 3;
       }

       if(next_ugly_no == next_multiple_of_5)
       {
           i5 = i5 + 1;
           next_multiple_of_5 = ugly[i5] * 5;
       }
    } 

    return next_ugly_no;
}
 
unsigned int min(unsigned int a, unsigned int b)
{
	return a < b ? a : b;
}

unsigned int Minimum(unsigned int a, unsigned int b, unsigned int c)
{
	unsigned int mini = min(a, b);

	return c < mini ? c : mini;
}