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;
    }
}