201. Bitwise AND of Numbers Rang

Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive.

For example, given the range [5, 7], you should return 4.

[26, 30]，它们的二进制如下：
左边公共部分决定了区间与的结果， 所以找到它再向左移回来。