number-of-bit-changes-to-make-two-integers-equal.cpp

// Time:  O(logn)
// Space: O(1)

// bit manipulation
class Solution {
public:
    int minChanges(int n, int k) {
        return (n & k) == k ? __builtin_popcount(n ^ k) : -1;
    }
};

// Time:  O(logn)
// Space: O(1)
// bit manipulation
class Solution2 {
public:
    int minChanges(int n, int k) {
        return (n | (n ^ k)) == n ? __builtin_popcount(n ^ k) : -1;
    }
};