Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

解：
2分搜索的应用，题目很简单，但要注意overflow的坑

class Solution {public:    int mySqrt(int x) {        int l=0;        int r=x;        while(l<r)        {            long mid=ceil((l+r+0LL)/2.0);            if(mid*mid*1LL==x)return mid;            else if(mid*mid*1LL>x)r=mid-1;            else            {                l=mid;            }        }        return l;    }};