[leetcode]Sqrt(x)

binary search

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