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;
}