LeetCode Divide Two Integers

class Solution {

public:

    int divide(int dividend, int divisor) {

        bool aneg = dividend < 0;

        bool bneg = divisor < 0;

        unsigned int a = dividend;

        unsigned int b = divisor;

        if (aneg) a = ~(a - 1);

        if (bneg) b = ~(b - 1);

        unsigned int oa = a, ob = b;

        if (b > a || a == 0) return 0;



        unsigned int abits = 0, bbits = 0;

        while (a) a>>=1, abits++;

        while (b) b>>=1, bbits++;

        a = oa, b = ob;

        unsigned int a_high_bit = 1<<(abits-1);

        unsigned int mask = a_high_bit;

        for (int i=bbits-1; i>0; i--) {

            mask = a_high_bit | (mask>>1);

        }

        unsigned int res = 0;

        unsigned int r_mask = 1<<(abits - bbits);

        b = b<<(abits - bbits);

        while (r_mask) {

            if ((mask & a) >= (mask & b)) {

                res |= r_mask;

                a = a - b;

            }

            mask = (mask>>1)|a_high_bit;

            r_mask>>=1;

            b>>=1;

        }

        if (aneg^bneg)

            return -res;

        else

            return res;

    }

};

犹记得当年计组的时候手工做过，如果不用long的话，在有符号和无符号之间转换要非常小心

参考：

　　http://blog.csdn.net/feiyangyangfei/article/details/9214107