29. Divide Two Integers【递归+位运算】

refer: https://leetcode.com/problems/divide-two-integers/

package LeetCode;

public class Test {
	public static void main(String[] args) {
		System.out.println(Integer.MIN_VALUE >> 1);
		System.out.println(Integer.MIN_VALUE);
	}
	
	// 位运算 + 递归实现
		// 思路 : 所有的数字都可以用二进制来表示
		/* 计算过程如下
		 * 100/2 = 2*32 + 2*16 + 2*2;
		 * 32+16+2 = 50
		 * 100/3 = 3*32 + 3*1
		 * 32 + 1 = 33
		*/

    public int divide(int dividend, int divisor) {
    	if (dividend == Integer.MIN_VALUE && divisor == -1)
    		return Integer.MAX_VALUE;
    	
    	int positiveDividend = dividend > 0 ? -dividend : dividend;
    	int positiveDivisor = divisor > 0 ? -divisor : divisor;
    	
    	int leftTime = 0;
    	int result = 0;
    	
    	int maxRight1 = Integer.MIN_VALUE >> 1;
    	
    	if (dividend == 0 || positiveDividend - positiveDivisor > 0)
    		return 0;
    	
    	while (positiveDividend - positiveDivisor < 0) {
    		
    		if (positiveDivisor < maxRight1 || positiveDividend - (positiveDivisor << 1) > 0) break;
    		
			positiveDivisor = positiveDivisor << 1;
			leftTime ++;
    	}
    	
    	// 递归
		result = (1 << leftTime) 
				+ divide(positiveDividend - positiveDivisor, divisor > 0 ? 0 - divisor : divisor);
		if ((dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0)) {
			result = 0 - result;
		}
		return result;
    }
}