Hackerrank "maximizing XOR"

A natural thought is brutal-force. But as you may have already thought of, there must be a smarter one. And yes there is.

Think like this: XOR gives you all different bits, if you cocould imagine the binary representation of L ^ r, it can be represented as: 1xxxxx... what is asked is the 'maximum 'value of L ^ r-and that means 1111111... so this maximum value only depends on which is the highest 1-it is irrelevant with all intermediate values. so now the question turns to be: Which is the highest bit of (L ^ r )?

Then an more elegant solution comes:

Int maxxor (int l, int R) {size_t bitlen = floor (log (L ^ r)/log (2); Return (2 <bitlen)-1 ;}

Lesson Learned: Make bit operations meaningful

Hackerrank "maximizing XOR"