【Leetcode】Divide Two Integers

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

class Solution {
public:
    int divide(int dividend, int divisor) {
        long long a = dividend < 0 ? -(long long)dividend : dividend;
        long long b = divisor < 0 ? -(long long)divisor : divisor;
        bool sign = (dividend >= 0 && divisor >= 0) || 
                    (dividend <= 0 && divisor <= 0);
        long long ans = 0;
        while (a >= b) {
            long long c = b;
            for (int i = 0; c <= a; c = c << 1, ++i) {
                a -= c;
                ans += (1 << i);
            }
        }
        return sign ? ans : -ans;
    }
};

不能用乘、除和取模，那么还可以用加、减和移位。

符号单独考虑。主要从减法出发，可以通过移位加倍被除数从而实现加速。有一点要特别注意的是可能发生溢出，需要用long long类型来进行中间的运算。