LeetCode 029 Divide Two Integers

题目要求：Divide Two Integers

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

If it is overflow, return MAX_INT.

分析：

不能用乘、除和取余，则只能用减了……

代码如下：

class Solution {
public:
    int divide(int dividend, int divisor) {

        // 当 dividend = INT_MIN 时， -dividend 会溢出，所以用 long long
        long long a = dividend >= 0 ? dividend : -(long long)dividend;
        long long b = divisor >= 0 ? divisor : -(long long)divisor;

        const bool sign = (dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0); // 异号

        // 当 dividend = INT_MIN 时， divisor = -1 时，结果会溢出，所以用 long long
        long long result = 0;

        while (a >= b) {
            long long c = b;
            for (int i = 0; a >= c; ++i, c <<= 1) {
                a -= c;
                result += 1 << i;
            }
        }

        if(sign == 0 && result >= 2147483647) result = 2147483647;
        if(sign == 1 && result <= -2147483647) result = -2147483647;

        return ((dividend^divisor) >> 31) ? (-result) : (result);

    }
};