Divide two integers without using multiplication, division and mod operator.

If it is overflow, return MAX_INT.

题目要求不能使用除号、乘号和取余操作符。

我们使用移位操作符。<< 左移代表乘以2，>>右移代表除以2

//a，b分别为被除数和除数    public int divide(int a,int b){        long res=0;        int sign = 1;        if((a<0 && b>0)||(a>0&&b<0)){            sign = -1;        }        if(b==0||(a==Integer.MIN_VALUE&&b==-1)){            return Integer.MAX_VALUE;        }        if(a
      
       b){            long temp = b;            long p = 1;            while(a>=(temp<<1)){                temp<<=1;                p<<=1;            }            a-=temp;            res+=p;        }        res = sign*res;        return (int) res;    }