Leetcode[201] Bitwise AND of Numbers Range

###Task1 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.

###Python

class Solution(object):
    def rangeBitwiseAnd(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        pos = 0
        while m != n:
            m >>= 1
            n >>= 1
            pos += 1
        return m << pos

###Points

由数据范围0 <= m <= n <= 2147483647可知，时间复杂度O（n）及以上的解法是不可接受的。

因此可以判断此题为数学题。

参考LeetCode Discuss链接：https://leetcode.com/discuss/32053/accepted-c-solution-with-simple-explanation

[m, n]范围的按位与的结果为m与n的公共“左边首部（left header）”