Java [leetcode 29]Divide Two Integers

题目描述：

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

If it is overflow, return MAX_INT.

解题思路：

把除数表示为：dividend = 2^i * divisor + 2^(i-1) * divisor + ... + 2^0 * divisor。这样一来，我们所求的商就是各系数之和了，而每个系数都可以通过移位操作获得。

详细解说请参考：http://blog.csdn.net/whuwangyi/article/details/40995863

代码如下：

public class Solution {

    public int divide(int dividend, int divisor) {

		boolean flag = (dividend > 0 && divisor > 0)

				|| (dividend < 0 && divisor < 0);

		long absDividend = Math.abs((long) dividend);

		long absDivisor = Math.abs((long) divisor);

		long quotient = dividePositive(absDividend, absDivisor);

		if (flag && quotient > Integer.MAX_VALUE)

			return Integer.MAX_VALUE;

		return flag ? (int) quotient : -(int) quotient;

	}

	public long dividePositive(long dividend, long divisor) {

		if (dividend < divisor)

			return 0;

		long quotient = 1;

		long originalDivisor = divisor;

		while (dividend >= (divisor << 1)) {

			quotient <<= 1;

			divisor <<= 1;

		}

		return quotient + dividePositive(dividend - divisor, originalDivisor);

	}

}