《剑指offer》第四十九题（丑数）

// 面试题49：丑数
// 题目：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。

#include <iostream>

// ====================算法1的代码====================
//不用额外的内存，直接计算
bool IsUgly(int number)//判断是不是丑数
{
    while (number %  == )
        number /= ;
    while (number %  == )
        number /= ;
    while (number %  == )
        number /= ;

    return (number == ) ? true : false;
}

int GetUglyNumber_Solution1(int index)
{
    if (index <= )
        return ;

    int number = ;
    int uglyFound = ;
    while (uglyFound < index)//从头到尾开始计算
    {
        ++number;

        if (IsUgly(number))
            ++uglyFound;
    }

    return number;
}

// ====================算法2的代码====================
//使用内存，只计算丑数，节省时间
int Min(int number1, int number2, int number3);

int GetUglyNumber_Solution2(int index)
{
    if (index <= )
        return ;

    int *pUglyNumbers = new int[index];
    pUglyNumbers[] = ;
    int nextUglyIndex = ;

    int *pMultiply2 = pUglyNumbers;//用来存储前面丑数的二倍值中，刚好大于当前最大丑数的数值
    int *pMultiply3 = pUglyNumbers;//三倍
    int *pMultiply5 = pUglyNumbers;//五倍

    while (nextUglyIndex < index)
    {
        int min = Min(*pMultiply2 * , *pMultiply3 * , *pMultiply5 * );//将这三个值中最小值作为下一个丑数存储
        pUglyNumbers[nextUglyIndex] = min;

        while (*pMultiply2 *  <= pUglyNumbers[nextUglyIndex])//更新这三个值
            ++pMultiply2;
        while (*pMultiply3 *  <= pUglyNumbers[nextUglyIndex])
            ++pMultiply3;
        while (*pMultiply5 *  <= pUglyNumbers[nextUglyIndex])
            ++pMultiply5;

        ++nextUglyIndex;
    }

    int ugly = pUglyNumbers[nextUglyIndex - ];
    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;
}

// ====================测试代码====================
void Test(int index, int expected)
{
    if (GetUglyNumber_Solution1(index) == expected)
        printf("solution1 passed\n");
    else
        printf("solution1 failed\n");

    if (GetUglyNumber_Solution2(index) == expected)
        printf("solution2 passed\n");
    else
        printf("solution2 failed\n");
}

int main(int argc, char* argv[])
{
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    Test(, );
    system("pause");
    return ;
}