69.Sqrt(x)

int sqrt(int x)

class Solution {
public:
int mySqrt(int x) {
int left = 1;
int right = x >>1;
int mid;
int lastMid;

if(x < 2)
return x;
while(left <= right)
{
mid = (left + right) >>1;
if(x / mid > mid)
{
left = mid + 1;
lastMid = mid;
}
else if( x / mid < mid)
{
right = mid - 1;
}
else
return mid;
}

return lastMid;

}
};