给定一个数组，求子数组的最大异或和

public class Main {
    public static class Node {
        public Node[] nexts = new Node[2]; // 0,1
    }
    
    public static class NumTrie {
        public Node head = new Node();
        
        public void add(int num) {
            Node cur = head;
            for(int move = 31;move >= 0;move--) {
                int path = ((num >> move) & 1);//每一位上的数字(0,1)
                cur.nexts[path] = (cur.nexts[path] == null ? new Node() : cur.nexts[path]);
                cur = cur.nexts[path];
            }
        }
        
        public int maxXor(int num) {//num=0~i的异或结果
            Node cur = head;
            int res = 0;
            for(int move = 31;move >= 0;move--) {
                int path = (num >> move) & 1;//提取每一位
                int best = (move == 31 ? path : (path ^ 1));//最高位期望一样，非最高位期望相反
                best = cur.nexts[best] != null ? best : (best ^ 1);//实际要选的路（如果没有期待选的路）
                res |= (path ^ best) << move;//设置答案的每一位
                cur = cur.nexts[best];//继续往下走
            }
            return res;
        }
    }
    public static int maxXorSubArray(int[] arr) {
        if (arr == null || arr.length == 0) 
            return 0;
        int max = Integer.MIN_VALUE;
        int xor = 0;
        NumTrie numTrie = new NumTrie();
        numTrie.add(0);
        for(int i = 0;i < arr.length;i++) {
            xor ^= arr[i];
            max = Math.max(max,numTrie.maxXor(xor));
            numTrie.add(xor);
        }
        return max;
    }
}