201. 数字范围按位与

//n & n-1 总是去掉二进制最低位的1 从最高位&起来会快很多
class Solution 
{
public:
    int rangeBitwiseAnd(int m, int n) 
    {
        //m <= n && m <= n - 1 ——> m <= n - 1
        while(m <= n - 1) n = n & (n - 1);
        return n;
    }
};