421. Maximum XOR of Two Numbers in an Array

class Solution {
    public int findMaximumXOR(int[] nums) {
        if(nums == null || nums.length < 2) return 0;
        Node r = new Node();
        int max = nums[0];
        for(int k : nums)
        {
            Node root = r;
            max = Math.max(max, k);
            for(int i = 31; i >= 0; i--)
            {
                if((k & (1 << i)) != 0)
                {
                    if(root.left == null) root.left = new Node();
                    root = root.left;
                }
                else
                {
                    if(root.right == null) root.right = new Node();
                    root = root.right;
                }
            }
        }
        int xor = 0;
        for(int k : nums)
        {
            Node root = r;
            int curxor = 0;
            for(int i = 31; i >= 0; i--)
            {
                curxor <<= 1;
                if((k & (1 << i)) != 0)
                {
                    if(root.right != null) root = root.right;
                    else
                    {
                        root = root.left;
                        curxor |= 1;
                    }
                }
                else
                {
                    if(root.left != null)
                    {
                        root = root.left;
                        curxor |= 1;
                    }
                    else root = root.right;
                }
            }
            xor = Math.max(xor, k ^ curxor);
        }
        return xor;
    }
}

class Node
{
    Node left, right;
}