【LeetCode 69】Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

思路：

　　突然发现，二分真TM的是万能的。还有牛顿迭代法，数学的东西，头疼不想看了。还有传说中的“魔数”法，比math库效率都高，试了下RE - -。

C++:

class Solution {
public:
    int mySqrt(int x) {
        
        if(x < 0)
            return 0;
        if(x == 0 || x == 1)
            return x;
        
        unsigned long long beg = 0;
        unsigned long long end = (x + 1) / 2;
        unsigned long long mid = 0; 
        unsigned long long mids = 0;
        
        while(beg < end)
        {
            mid = beg + (end - beg)/2;
            mids = mid * mid;
            
            if(mids == x)
            {
                return mid;
            }
            else if(mids > x)
            {
                end = mid - 1;
            }
            else
            {
                beg = mid + 1;
            }
        }
        
        mids = end * end;
        if(mids > x)
            return end - 1;
        else
            return end;
    }
};