让O(n)来得更凶猛吧
Given a non-empty array of numbers, a0, a1, a2, … , an-1, where 0 ≤ ai < 2^31.

Find the maximum result of ai XOR aj, where 0 ≤ i, j < n.

Could you do this in O(n) runtime?

Example:

Input: [3, 10, 5, 25, 2, 8]

Output: 28

Explanation: The maximum result is 5 ^ 25 = 28.