69.x 的平方根 (Easy)*

class Solution {
public:
    int mySqrt(int x) {
        if(x <= 1) {
            return x;
        }
        int l = 1, r = x;
        int mid = 0;
        int sqrt = 0;
        while(l <= r) {
            mid = l + (r - l) / 2;
            sqrt = x / mid;
            if(sqrt == mid) {
                return mid;
            }else if(mid > sqrt) {
                r = mid - 1;
            }else {
                l = mid + 1;
            }
        }
        return r;
    }
};