[leetcode]Sqrt(x)

class Solution {

public:

    int sqrt(int x) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        if(x < 1) return 0;

        if(x == 1) return 1;

        

        int start = 1;

        int end = x;

        

        int mid;

        while(start <= end){

            mid = (start + end)/2;

            

            if(x / mid == mid) return mid;

            if(mid < x/mid) start = mid +1;

            else end = mid -1;

            

        }

        

        return (start + end)/2;

    }

};