// 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 % 2 == 0)number /= 2;while (number % 3 == 0)number /= 3;while (number % 5 == 0)number /= 5;return (number == 1) ? true : false;
}int GetUglyNumber_Solution1(int index)
{if (index <= 0)return 0;int number = 0;int uglyFound = 0;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 <= 0)return 0;int *pUglyNumbers = new int[index];pUglyNumbers[0] = 1;int nextUglyIndex = 1;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 * 2, *pMultiply3 * 3, *pMultiply5 * 5);//将这三个值中最小值作为下一个丑数存储pUglyNumbers[nextUglyIndex] = min;while (*pMultiply2 * 2 <= pUglyNumbers[nextUglyIndex])//更新这三个值++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;
}// ====================测试代码====================
void Test(int index, int expected)
{if (GetUglyNumber_Solution1(index) == expected)printf("solution1 passed\n");elseprintf("solution1 failed\n");if (GetUglyNumber_Solution2(index) == expected)printf("solution2 passed\n");elseprintf("solution2 failed\n");
}int main(int argc, char* argv[])
{Test(1, 1);Test(2, 2);Test(3, 3);Test(4, 4);Test(5, 5);Test(6, 6);Test(7, 8);Test(8, 9);Test(9, 10);Test(10, 12);Test(11, 15);Test(1500, 859963392);Test(0, 0);system("pause");return 0;
}