leetcode: Divide Two Integers

将因子不断乘以2（可以通过移位实现，同时结果也从1开始不断移位加倍），然后和被除数比较，等到大于被除数一半了，就从被除数中减去，将因子个数叠加入结果中。然后在剩下的被除数中采用同样的方法减去小于其一半的因子和，循环往复

必须要unsigned int

class Solution {
public:
int divide(int dividend, int divisor) {
assert( divisor != 0);
int res = 0;
bool neg = (( dividend ^ divisor) >> ( sizeof(int) * 8 - 1)) ? false : true;
unsigned tdividend = abs(dividend);
unsigned tdivisor = abs(divisor);
while( tdividend > tdivisor){
int factor = 1;
unsigned tmp = tdivisor;
while( (tmp<<= 1) < tdividend){
factor <<= 1;
}
tdividend -= ( tmp >>= 1);
res += factor;
}
if( tdividend == tdivisor)
++res;
return neg ? res : -res;
}
};