给定一个数组，求子数组的最大异或和

public static int getMaxEOR1(int[] arr){
    int max = Integer.MIN_VALUE;
    for (int i = 0 ; i < arr.length ;i++){
        for (int start = 0 ;start <= i;start++) {
            int res = 0;
            for (int j = start; j <= i; j++) {
                res ^= arr[j];
            }
            max = Math.max(max, res);
        }
    }
    return max;
}

    public static int getMaxEOR2(int[] arr){
        int max = Integer.MIN_VALUE;
        int[] dp = new int[arr.length];
        int eor = 0;
        for (int i = 0 ; i < arr.length; i++){
            eor ^= arr[i];  // 0 .. i 的异或和
            max = Math.max(max,eor);  // 由于下面的start的初始为1 没有包括0 ，
                                      // 所以这里需要将0..i的包括进来
            for (int start = 1 ; start <= i ;start++){ 
                //求的是start .. i 的异或和 ，start = 1 .. i
                int curROR = eor ^ dp[start - 1];
                max = Math.max(max,curROR);
            }
            dp[i] = eor;
        }
        return max;
    }

public static class Node {
   public Node[] nexts = new Node[2];
}

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);
         cur.nexts[path] = cur.nexts[path] == null ? new Node() : cur.nexts[path];
         cur = cur.nexts[path];
      }
   }

   public int maxXor(int num) {
      Node cur = head;
      int res = 0;
      for (int move = 31; move >= 0; move--) {
         int path = (num >> move) & 1;
         int best = move == 31 ? path : (path ^ 1);
         best = cur.nexts[best] != null ? best : (best ^ 1);
         res |= (path ^ best) << move;
         cur = cur.nexts[best];
      }
      return res;
   }

}

public static int maxXorSubarray(int[] arr) {
   if (arr == null || arr.length == 0) {
      return 0;
   }
   int max = Integer.MIN_VALUE;
   int eor = 0;
   NumTrie numTrie = new NumTrie();
   numTrie.add(0);
   for (int i = 0; i < arr.length; i++) {
      eor ^= arr[i];
      max = Math.max(max, numTrie.maxXor(eor));
      numTrie.add(eor);
   }
   return max;
}