LeetCode | Divide Two Integers

题目

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

分析

逐个减太慢，肯定超时。需要指数级增加后再减，思想类似于Linked List Cycle II中的Brent方法。

此外，还要注意零、负数的情况。

代码

public class DivideTwoIntegers {
	public int divide(int dividend, int divisor) {
		if (dividend == 0 || divisor == 0) {
			return 0;
		}
		boolean isNeg = (dividend > 0 && divisor < 0)
				|| (dividend < 0 && divisor > 0);
		long a = Math.abs((long) dividend);
		long b = Math.abs((long) divisor);
		if (b > a) {
			return 0;
		}

		long sum = 0;
		long pow = 0;
		int result = 0;
		while (a >= b) {
			pow = 1;
			sum = b;
			while (sum + sum <= a) {
				sum += sum;
				pow += pow;
			}
			a -= sum;
			result += pow;
		}
		return isNeg ? -result : result;
	}
}