Divide two integers without using multiplication, division and mod operator.
不使用乘法、除法和求模运算求两个数相除。
class Solution {
public:
long long internalDivide(unsigned long long dividend,unsigned long long divisor)
{
if(dividend<divisor)
return 0;
int result = 1;
unsigned long long temp = divisor,left;
while(temp<=dividend)
{
left = dividend - temp;
temp<<=1;
if(temp>dividend)
break;
else
result<<=1;
}
return result + internalDivide(left,divisor);
}
int divide(int dividend, int divisor) {
unsigned long long _dividend = abs(static_cast<long long>(dividend)),
_division = abs(static_cast<long long>(divisor));
bool flag = ((dividend<=0)&&(divisor>0))|| ((dividend>=0)&&(divisor<0));
return flag?(-1)*internalDivide(_dividend,_division):internalDivide(_dividend,_division);
}
};
简要分析，以87/4为例：4小于87,4左移一位变成8，计数左移一位变成2。8小于87，继续左移变成16，计数变成4.16小于87左移变成32，计数变成8。32小于87左移变成64，计数变成16。继续左移变成128大于87。87减去64 = 23。计数为16倍。用23继续上述步骤，知道
