华为9.9第三题

import java.util.HashMap;
import java.util.Scanner;

public class Main {
    static int result = 0;
    public static class TreeNode{
        int id;
        int value;
        int left_id;
        int right_id;
        TreeNode left;
        TreeNode right;
        public TreeNode() {

        }
        public TreeNode(int id, int value) {
            this.id = id;
            this.value = value;
        }

        public TreeNode(int id, int value, int left_id, int right_id) {
            this.id = id;
            this.value = value;
            this.left_id = left_id;
            this.right_id = right_id;
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        HashMap<Integer,TreeNode> map = new HashMap<>();
        for(int i =0;i<n;i++){
            int node_id = sc.nextInt();
            int node_value = sc.nextInt();
            int left_id = sc.nextInt();
            int right_id = sc.nextInt();
            TreeNode treeNode = new TreeNode(node_id,node_value,left_id,right_id);
            map.put(node_id,treeNode);
        }
        for(Integer key:map.keySet()){
            TreeNode treeNode = map.get(key);
            if(treeNode.left_id!=-1){
                treeNode.left = map.get(treeNode.left_id);
            }
            if(treeNode.right_id!=-1){
                treeNode.right = map.get(treeNode.right_id);
            }
        }
        for(Integer key:map.keySet()){
            TreeNode treeNode = map.get(key);
            dfs(treeNode,0);
        }
        System.out.println(result);


    }
    public static void dfs(TreeNode node,int value){
        if(node==null){
            return;
        }
        value = value^node.value;
        if(value>result){
            result = value;
        }
        dfs(node.left,value);
        dfs(node.right,value);
    }
}