算法-二分法-两数相除

class Solution {
    
    
   public int divide(int dividend, int divisor) {
    
     // 被除数 除数
        if(divisor == -1 && dividend == Integer.MIN_VALUE) 
        return Integer.MAX_VALUE; // 溢出
        int sign = 1;
        if((dividend > 0 && divisor < 0)||(dividend < 0 && divisor > 0))
            sign = -1;
       // if(divisor == 1) return dividend;
        // if(divisor == -1) return -dividend;
        int a = dividend>0 ? -dividend : dividend;
        int b = divisor>0 ? -divisor : divisor;
        // 都改为负号是因为int 的范围是[2^31, 2^31-1]，如果a是-2^32，转为正数时将会溢出
        //System.out.println(a + " " + b);
        if(a > b) return 0;
        int ans = div(a,b);
        return sign == -1 ? -ans : ans;
    }
    int div(int a, int b)
    {
    
    
        if(a > b) return 0;
        int count = 1;
        int tb = b;
        while(tb+tb >= a && tb+tb < 0){
    
     // 溢出之后不再小于0
            tb += tb;
            count += count;
            //System.out.println(tb + " " + count + " " + count*b);
        }
        return count+div(a-tb,b);
    }
}