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.
Credits:Special thanks to @amrsaqr for adding this problem and creating all test cases.
在草稿纸上，演算以下两组参数，就可以明白程序的用意了。 1.
m = 5, n = 7
5 : 0101
6 : 0110
7 : 0111
结果
4 : 0100
m = 6, n = 8
6 : 0110
7 : 0111
8 : 1000
结果
0 : 0000