29. 两数相除 Divide Two Integers

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator.

Return the quotient after dividing dividend by divisor.

The integer division should truncate toward zero, which means losing its fractional part. For example, truncate(8.345) = 8 and truncate(-2.7335) = -2.

Note:

Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−2^31, 2^31 − 1]. For this problem, assume that your function returns 2^31 − 1 when the division result overflows.

方法：

1.注意溢出，可以转换成负值处理。

2.和divisor倍数比较

public int divide(int dividend, int divisor){
        if (divisor == 0) return Integer.MAX_VALUE;
        if(dividend == 0) return 0;
        if(divisor == -1){
            if(dividend > Integer.MIN_VALUE) return -dividend;
            return Integer.MAX_VALUE;
        }else if(divisor == 1){
            return dividend;
        }

        int result = 0;
        int sign = -1;
        if (dividend > 0 && divisor > 0 || dividend < 0 && divisor < 0) sign =  1;
        if (dividend > 0) dividend = -dividend;
        if (divisor > 0) divisor = -divisor;
        while ( dividend<=divisor){
            int temp=divisor;
            int c=1;
            while(dividend-temp<=temp) {
                temp=temp<<1;
                c=c<<1;
            }
            dividend-=temp;
            result+=c;
        }
        return  sign > 0 ? result : -result;
    }