根据数组层次遍历构建二叉树

最新推荐文章于 2024-05-14 18:27:26 发布

原创最新推荐文章于 2024-05-14 18:27:26 发布 · 1.1k 阅读

2 ·

CC 4.0 BY-SA版权

文章标签：

#构建树

二叉树专栏收录该内容

13 篇文章

订阅专栏

本文介绍了一个使用Java实现的二叉树数据结构，并通过层次遍历的方式获取指定层级的节点值，展示了如何构建二叉树、进行层次遍历以及输出特定范围内的层级数据。

/**
    15
    15 7 20 -1 -1 3 12 -1 -1 -1 -1 14 8 -1 -1
    2 4
*/
import java.util.*;

public class Main2 {
    static int[]  value ;
    static class TreeNode{
        int val;
        TreeNode left,right;
        public TreeNode(int t) {
            this.val =t;
        }
    }
    static ArrayList<ArrayList<Integer>> rs;
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int n = cin.nextInt();
         value = new int[n];
        for(int i = 0;i < n;i++) {
             value[i] = cin.nextInt();
        }
        int s = cin.nextInt();
        int e = cin.nextInt();
        TreeNode head = getTree();
        getRs(head,s,e);
        for(ArrayList list : rs) {
            for(int i = 0;i < list.size();i++) {
                if(i == list.size() -1) {
                    System.out.println(list.get(i));
                } else {
                    System.out.print(list.get(i) +" ");
                }
            }
        }
    }



    private static void getRs(TreeNode root, int s, int e) {
        rs = new ArrayList();
        LinkedList<TreeNode> queue= new LinkedList();
        if(root == null) {
            return;
        }
        queue.offer(root);
        int ceng = 1;
        while(queue.size() > 0) {
            int size=queue.size();
            ArrayList<Integer> list=new ArrayList<>();

            for (int i = 0; i < size; i++) {
                TreeNode top = queue.poll();
                if (top == null || top.val == -1) {
                    continue;
                }
                list.add(top.val);
                queue.add(top.left);
                queue.add(top.right);
            }
            if(ceng >= s && ceng <= e) {
                rs.add(new ArrayList<>(list));
            }

            ceng++;
        }
    }


    private static TreeNode getTree(){
        TreeNode  p = new TreeNode(value[0]);
        TreeNode  q = p;
        Queue<TreeNode > queue = new LinkedList();
        int i = 0;
        while (p != null) {
            if(2*i+1<value.length){
                p.left = new TreeNode(value[2 * i + 1]);
                queue.add(p.left);
            }
            if (2*i+2<value.length){
                p.right = new TreeNode(value[2 * i + 2]);
                queue.add(p.right);
            }
            p = queue.poll();
            i++ ;
        }
        return q;
    }
}