34丑数

标签：数组

bool IsUgly(int number)
{
while (number % 2 == 0)
number /= 2;
while (number % 3 == 0)
number /= 3;
while (number % 5 == 0)
number /= 5;
return (number == 1) ? true : false;
}

接下来只需要按顺序判断每一个整数是不是丑数，代码如下：

int GetUglyNumber(int index)
{
if (index <= 0)
return 0;
int number = 0;
int uglyFound = 0;
while (uglyFound < index)
{
++number;
if (IsUgly(number))
{
++uglyFound;
}
}
return number;
}

只需要在函数GetUglyNumber中传入参数1500，就能得到第1500个丑数。但是每个整数都需要做求余和除法运算，时间效率不是很高。

int GetUglyNumber_Solution2(int index)
{
if (index <= 0)
return 0;
int *pUglyNumbers = new int[index];
pUglyNumbers[0] = 1;
int nextUglyIndex = 1;
int* pMultiply2 = pUglyNumbers;
int* pMultiply3 = pUglyNumbers;
int* pMultiply5 = pUglyNumbers;
while (nextUglyIndex < index)
{
int min = Min(*pMultiply2 * 2, *pMultiply3 * 3, *pMultiply5 * 5);
pUglyNumbers[nextUglyIndex] = min;
while (*pMultiply2 * 2 <= pUglyNumbers[nextUglyIndex])
   ++pMultiply2;
while (*pMultiply3 * 3 <= pUglyNumbers[nextUglyIndex])
++pMultiply3;
while (*pMultiply5 * 5 <= pUglyNumbers[nextUglyIndex])
++pMultiply5;
++nextUglyIndex;
}
int ugly = pUglyNumbers[nextUglyIndex - 1];
delete[] pUglyNumbers;
return ugly;
}
int Min(int number1, int number2, int number3)
{
int min = (number1 < number2) ? number1 : number2;
min = (min < number3) ? min: number3;
return min;
}

34丑数

标签：数组

原文地址：http://blog.csdn.net/wangfengfan1/article/details/46830549