[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;
}
};