【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++:

 1 class Solution {
 2 public:
 3     int mySqrt(int x) {
 4
 5         if(x < 0)
 6             return 0;
 7         if(x == 0 || x == 1)
 8             return x;
 9
10         unsigned long long beg = 0;
11         unsigned long long end = (x + 1) / 2;
12         unsigned long long mid = 0;
13         unsigned long long mids = 0;
14
15         while(beg < end)
16         {
17             mid = beg + (end - beg)/2;
18             mids = mid * mid;
19
20             if(mids == x)
21             {
22                 return mid;
23             }
24             else if(mids > x)
25             {
26                 end = mid - 1;
27             }
28             else
29             {
30                 beg = mid + 1;
31             }
32         }
33
34         mids = end * end;
35         if(mids > x)
36             return end - 1;
37         else
38             return end;
39     }
40 };