LeetCode 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.

For example, given the range [5, 7], you should return 4.

 1 class Solution {
 2 public:
 3     int rangeBitwiseAnd(int m, int n) {
 4         int res = 0;
 5         
 6         for (int i=0; i<32 && (n!= 0 && m != 0); i++) {
 7             res = res | (bitvalue(m, n) << i);
 8             m>>=1;
 9             n>>=1;
10         }
11         return res;
12     }
13     
14     int bitvalue(int m, int n) {
15         if (n - m > 0) {
16             return 0;
17         }
18         if (n == m && (n&0x1 == 1)) {
19             return 1;
20         }
21         return 0;
22     }
23 };

都忘了自己第一次是怎么想出来的了，看了discuss的一种解法：

class Solution {
public:
    int rangeBitwiseAnd(int m, int n) {
        int x = m^n;
        int cnt = 0;
        while (x) {
            cnt++;
            x>>=1;
        }
        return (m & n) & ~((1<<cnt) - 1);
    }
};

简单很多