Leetcode: Divide Two Integers

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

用减法：Time Limit Exceeded

 

int divide(int dividend, int divisor) {
        // Note: The Solution object is instantiated only once.
        int res = 0;
		if(divisor == 0) return 0;
		if(divisor==1)return dividend;
		else if(divisor == -1)return -dividend;

		bool ispositive = true;
		if(dividend<0)
		{
			dividend = -dividend;
			if(divisor<0)
				divisor = -divisor;
			else
				ispositive = false;
		}
		else if(divisor<0)
		{
			divisor = -divisor;
			ispositive = false;
		}
		while(dividend>=divisor)
		{
		    dividend -= divisor;
			res++;
		}
		if(!ispositive)
			res = -res;
		return res;
    }

 

减法+位操作：Accepted

 

int divide(int dividend, int divisor) {
        // Note: The Solution object is instantiated only once.
        long long a = abs((double)dividend);
		long long b = abs((double)divisor);
		long long res = 0;
		while(a >= b)
		{
			long long c = b;
			for(int i = 0; a >= c; i++, c <<=1)
			{
				a -= c;
				res += 1<<i;
			}
		}
		return ((dividend ^ divisor) >> 31) ? (-res) : (res);
    }