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.

class Solution {
public:
    int rangeBitwiseAnd(int m, int n) {
        int res = 0;
        
        for (int i=0; i<32 && (n!= 0 && m != 0); i++) {
            res = res | (bitvalue(m, n) << i);
            m>>=1;
            n>>=1;
        }
        return res;
    }
    
    int bitvalue(int m, int n) {
        if (n - m > 0) {
            return 0;
        }
        if (n == m && (n&0x1 == 1)) {
            return 1;
        }
        return 0;
    }
};

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