201. Bitwise AND of Numbers Range

https://leetcode.com/problems/bitwise-and-of-numbers-range/

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

解题思路：

先硬来，超时。

看大神的解法，结论是这道题其实就是要找m和n的bit common prefix。而不需要从m一直算到n。

The hardest part of this problem is to find the regular pattern.
For example, for number 26 to 30
Their binary form are:
11010
11011
11100　　
11101　　
11110

https://leetcode.com/problems/bitwise-and-of-numbers-range/discuss/56729/Bit-operation-solution(JAVA)

class Solution {
    public int rangeBitwiseAnd(int m, int n) {
        int step = 0;
        while (m != n) {
            m = m >> 1;
            n = n >> 1;
            step++;
        }
        m = m << step;
        return m;
    }
}