Divide Two Integers

    题意是计算a/b，其中a、b均为int，结果也要int。但是计算不允许使用乘法、除法、取模运算。

class Solution 

{

public:

    // Divide two unsigned int once, using binary divide method.

    unsigned int unsigned_divide_once(unsigned int &dividend, unsigned int divisor)

    {

        if (dividend < divisor)

        {

            dividend = 0; // Update dividend.

            return 0;

        }

        unsigned int result = 1;

        while (divisor < dividend)

        {

            divisor <<= 1;

            result <<= 1;

        }

        if (divisor != dividend)

        {

            divisor >>= 1;

            result >>= 1;

        }

        dividend -= divisor;

        return result;

    }

    int divide(int dividend, int divisor) 

    {

        if (divisor == 0) throw 1;

        bool negative = (dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0);

        unsigned int udividend = dividend < 0 ? -dividend : dividend;

        unsigned int udivisor = divisor < 0 ? -divisor : divisor;

        unsigned int uresult = 0;

        while (udividend != 0)

        {

            uresult += unsigned_divide_once(udividend, udivisor);

        }

        return negative ? -(int)uresult : (int)uresult;

    }

};