201. Bitwise AND of Numbers Range

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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

思路：
and 的话必须两个都是1才是1.
先看最后一位。
101
110
111

抹掉，再看下一位
10
11
11
第一位，都是1，一共抹掉2个0，所以 1<<2
1
1
1

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