答案

public class Solution {
    public int divide(int dividend, int divisor) {
        int result=0;
        int p=0;
        long currentSum=0;
        boolean positive=true;
        long fenmu=divisor;
        long fenzi=dividend;
        if(fenmu<0)
        {
            fenmu=-fenmu;
            if(fenzi<0){
                fenzi=-fenzi;
            }
            else{
                positive=false;
            }
        }
        else
        {
            if(fenzi<0){
                fenzi=-fenzi;
                positive=false;
            }
        }
        while(currentSum<fenzi)
        {
            if(p==0)
            {
                p++;
                currentSum+=fenmu;
            }
            else
            {
                if(fenzi-currentSum>currentSum)
                {
                    p+=p;
                    currentSum+=currentSum;
                }
                else
                {
                    result+=p;
                    fenzi-=currentSum;
                    p=0;
                    currentSum=0;
                }
            }
        }
        result+=p;
        fenzi-=currentSum;
        if(fenzi==0)
        {
            result=positive?result:-result;
        }
        else{
             result--;
             result=positive?result:-result;
        }
        return result;
    }
}