# Question

Given a range `[m, n]`

where `0 <= m <= n <= 2147483647`

, return the bitwise AND of all numbers in this range, inclusive.

Example 1:

```
Input: [5,7]
Output: 4
```

Example 2:

```
Input: [0,1]
Output: 0
```

# Solution

One bit can be set if and only if both m and n have this bit set, and the range is not larger than the number of this bit.

```
class Solution(object):
def rangeBitwiseAnd(self, m, n):
"""
:type m: int
:type n: int
:rtype: int
"""
res = 0
bit = 1
diff = n - m + 1
while m >= bit:
if m & bit != 0 and n & bit != 0 and diff <= bit:
res += bit
bit *= 2
return res
```