LeetCode 29. Divide Two Integers

LeetCode 29. Divide Two Integers

Solution1：
参考网址：[1]https://blog.youkuaiyun.com/qq_31617121/article/details/80458587
[2]http://www.cnblogs.com/grandyang/p/4431949.html
相当于复杂度优化到logN.
如 100 3
普通方法是 3 + 3 + 3 + 3 … + 3累加到100，数加了多少次
优化方法 3 6 12 24…
1 2 4 8… 看能累加多少次，超过的方法减去求得剩下的值，继续进行累加。
注意边界条件

class Solution {
public:
    int divide(int dividend, int divisor) {
        if (divisor == 0 || (dividend == INT_MIN && divisor == -1)) return INT_MAX;
        long long m = abs((long long)dividend), n = abs((long long)divisor), res = 0;
        int sign = ((dividend < 0) ^ (divisor < 0)) ? -1 : 1;
        if (n == 1) return sign == 1 ? m : -m;
        while (m >= n) {
            long long t = n, p = 1;
            while (m >= (t << 1)) {
                t <<= 1;
                p <<= 1;
            }
            res += p;
            m -= t;
        }
        return sign == 1 ? res : -res;
    }
};