29. Divide Two Integers

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

If it is overflow, return MAX_INT.

1、让divisor一直乘2

2、如果divisor>dividend，则用dividend - 上一个divisor

3、余下的数继续重复1，2步

这里有两种情况会溢出：

1、divisor = 0;
2、dividend = INT_MIN && divisor = -1 (因为 abs(INT_MIN) = INT_MAX + 1).

还有一点需要注意temp一直乘2会溢出，用long

dividend，divisor可能是Integer.MIN_VALUE，abs的时候会溢出int，用long缓存一下。abs时需要用java.lang.Math.abs(long a)防止溢出。

代码如下：

public class Solution {
    public int divide(int dividend, int divisor) {
        if (divisor == 0 || (dividend == Integer.MIN_VALUE && divisor == -1)) {
            return Integer.MAX_VALUE;
        }
        int sign = ((dividend < 0) ^ (divisor < 0)) ? -1 : 1;
        int result = 0;
        long divd = Math.abs((long)dividend);
        long div = Math.abs((long)divisor);
        while (divd >= div) {
            long mul = 1, temp = div;
            while (divd >= temp << 1) {
                temp = temp << 1;
                mul = mul << 1;
            }
            result += mul;
            divd -= temp;
        }
        return sign == -1? -result: result;
    }
}