面试题34：丑数

题目描述

我们把只包含因子2、3和5的数称作丑数（Ugly Number）。求按从小到大的顺序的第1500个丑数。例如6、8都是丑数，但14不是，因为它包含因子7.习惯上我们把1当做第一个丑数。

题目分析

剑指Offer（纪念版）P182

代码实现

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;
}