1. Divide Two Integers My Submissions QuestionEditorial Solution
   
   Total Accepted: 66073 Total Submissions: 421509 Difficulty: Medium
   
   Divide two integers without using multiplication, division and mod operator.

If it is overflow, return MAX_INT.

思路：每次减去b(同时b不断的翻倍，从1,2,2^2…)

为什么这样是可行的，因为如果a=nb+x

那么n作为一个整数一定是可以表示成 2m+2m−1+...+21+20

所以从20,21。。。依次减是可行的

#define IMAX numeric_limits<int>::max()

#define IMIN numeric_limits<int>::min()

class Solution {

     public:

          int divide(int dividend,int divisor) {

            assert(divisor!=0);

            int sign = (dividend<0&&divisor>0||dividend>0&&divisor<0)?-1:1;

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

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

            unsigned int c = b;

            int multi=0;

            while(a>=b){

                int i=1;

                while(a>=b){

                    a -=b;

                    multi+=i;

                    if(b<IMAX>>1){

                        b=b<<1;

                        i<<=1;

                    }

                }

                b=c;

            }

            if(sign>0&&multi==IMIN)return IMAX;

            else return multi*sign;

      }

};