每日算法之二十五：Divide Two Integers

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

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