Day 23: BST Level-Order Traversal

Task 
A level-order traversal, also known as a breadth-first search, visits each level of a tree's nodes from left to right, top to bottom. You are given a pointer, , pointing to the root of a binary search tree. Complete the levelOrderfunction provided in your editor so that it prints the level-order traversal of the binary search tree.

Hint: You'll find a queue helpful in completing this challenge.

Input Format

The locked stub code in your editor reads the following inputs and assembles them into a BST: 
The first line contains an integer,  (the number of test cases). 
The  subsequent lines each contain an integer, , denoting the value of an element that must be added to the BST.

Output Format

Print the  value of each node in the tree's level-order traversal as a single line of  space-separated integers.

Sample Input

6
3
5
4
7
2
1

Sample Output

3 2 5 1 4 7 

Explanation

The input forms the following binary search tree: 

We traverse each level of the tree from the root downward, and we process the nodes at each level from left to right. The resulting level-order traversal is , and we print these data values as a single line of space-separated integers.

풀이

package Day23;

class Node {
    Node left, right;
    int data;

    Node(int data) {
        this.data = data;
        left = right = null;
    }
}

package Day23;

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Solution {


    static void levelOrder(Node root) {
        Queue<Node> nodeQueue = new LinkedList<>();
        nodeQueue.add(root);

        while (!nodeQueue.isEmpty()){
            Node node = nodeQueue.poll();
            System.out.print(node.data + " ");
            if (node.left != null) nodeQueue.add(node.left);
            if (node.right != null) nodeQueue.add(node.right);
        }
    }

    public static Node insert(Node root, int data) {
        if (root == null) {
            return new Node(data);
        } else {
            Node cur;
            if (data <= root.data) {
                cur = insert(root.left, data);
                root.left = cur;
            } else {
                cur = insert(root.right, data);
                root.right = cur;
            }
            return root;
        }
    }

    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int T = sc.nextInt();
        Node root = null;
        while (T-- > 0) {
            int data = sc.nextInt();
            root = insert(root, data);
        }
        levelOrder(root);
    }
}