sqrt(x)

Use long instead of int to calculate.

code

class Solution {
public:
    int mySqrt(int x) {
        if(x <= 0)
        {
            return 0;
        }

        long s = 1;
        long e = x;

        while(s+1 < e)
        {
            long mid = s+(e-s)/2;
            if(mid*mid == x)
            {
                return mid;
            }
            else if(mid * mid < x)
            {
                s = mid;
            }
            else
            {
                e = mid;
            }
        }

        if(e * e < x)
        {
            return e;
        }
        else
        {
            return s;
        }

    }
};