https://leetcode.com/problems/sqrtx/
class Solution {
public:
    int mySqrt(int x) {
       if(x==0) return 0;
        
        int s=1;
        int e = x;
        int ans;
        while(s<=e){
            int mid = s + (e-s)/2;
            
            if(mid== x/mid){
                return mid;
            }else if(mid < x/mid){
                ans = mid;
                s = mid + 1;
            }else{
                e = mid - 1;
            }
        }
        return ans;
    }
};