打印二叉树中两个给定级别之间的所有节点

给定一棵二叉树，打印二叉树中两个给定级别之间的所有节点。逐层打印节点，即任何级别的节点都应该从左到右打印。

在上面的树中，如果起始级别为 2，结束级别为 3，则解决方案应打印：

2 3 
4 5 6 7 

注意：级别编号从 1 开始，即根节点在级别 1。

先决条件：水平顺序遍历。
这个想法是使用队列对树进行级别顺序遍历并跟踪当前级别。如果当前级别位于开始级别和结束级别之间，则打印该级别的节点。

算法：

levelordertraverse (root, startLevel, endLevel)
q -> empty queue
q.enqueue (root)
level -> 0
while (not q.isEmpty())
     size -> q.size()
     level = level + 1
     while (size)
          node -> q.dequeue()
          if (level between startLevel and endevel)
               print (node)
           if(node.leftnull)
                q.enqueue (node. left)
           if(node.leftnull)
                q.enqueue(node.right)
           size =size -1

下面是上述算法的实现：

C++

// C++ program for Print all nodes
// between two given levels in
// a binary tree
#include
using namespace std;
 
// Class containing left and right
// child of current node and key value
struct tree
{
 
    int data;
    tree *left, *right;
};
struct tree* newNode(int x)
{
    tree* temp = new tree;
    temp->data = x;
    temp->left = temp->right = NULL;
}
 
// Iterative function to print all
// nodes between two given
// levels in a binary tree
void printNodes(tree* root, int start, int end)
{
    if (root == NULL)
    {
        return;
    }
 
    // create an empty queue and
    // enqueue root node
    queue queue ;
    queue.push(root);
 
    // pointer to store current node
    tree *curr = NULL;
 
    // maintains level of current node
    int level = 0;
 
    // run till queue is not empty
    while (!queue.empty())
    {
        // increment level by 1
        level++;
 
        // calculate number of nodes in
        // current level
        int size = queue.size();
 
        // process every node of current level
        // and enqueue their non-empty left
        // and right child to queue
        while (size != 0)
        {
            curr = queue.front();
            queue.pop();
 
            // print the node if its level is
            // between given levels
            if (level >= start && level <= end)
            {
                cout << curr->data << " ";
            }
            if (curr->left != NULL)
            {
                queue.push(curr->left);
            }
 
            if (curr->right != NULL)
            {
                queue.push(curr->right);
            }
            size--;
        }
 
        if (level >= start && level <= end)
        {
            cout << ("\n");
        };
    }
}
 
// Driver Code
int main()
{
     
    tree *root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(3);
    root->left->left = newNode(4);
    root->left->right = newNode(5);
    root->right->left = newNode(6);
    root->right->right = newNode(7);
 
    /* Constructed binary tree is
        1
    / \
    2 3
    / \ / \
    4 5 6 7 */
 
    int start = 2, end = 3;
 
    printNodes(root, start, end);
}
 
// This code is contributed by Rajput-Ji

Java

// Java program for Print all nodes
// between two given levels in
// a binary tree
 
import java.util.LinkedList;
import java.util.Queue;
 
public class BinaryTree {
 
    // Class containing left and right
    // child of current node and key value
    static class Node {
 
        int data;
        Node left, right;
 
        public Node(int item)
        {
            data = item;
            left = right = null;
        }
    }
 
    // Root of the Binary Tree
    Node root;
    public BinaryTree()
    {
        root = null;
    }
 
    // Iterative function to print all
    // nodes between two given
    // levels in a binary tree
    void printNodes(Node root, int start, int end)
    {
        if (root == null) {
            return;
        }
 
        // create an empty queue and
        // enqueue root node
        Queue queue = new LinkedList();
        queue.add(root);
 
        // pointer to store current node
        Node curr = null;
 
        // maintains level of current node
        int level = 0;
 
        // run till queue is not empty
        while (!queue.isEmpty()) {
            // increment level by 1
            level++;
 
            // calculate number of nodes in
            // current level
            int size = queue.size();
 
            // process every node of current level
            // and enqueue their non-empty left
            // and right child to queue
            while (size != 0) {
                curr = queue.poll();
 
                // print the node if its level is
                // between given levels
                if (level >= start && level <= end) {
                    System.out.print(curr.data + " ");
                }
                if (curr.left != null) {
                    queue.add(curr.left);
                }
 
                if (curr.right != null) {
                    queue.add(curr.right);
                }
                size--;
            }
 
            if (level >= start && level <= end) {
                System.out.println("");
            };
        }
    }
 
    // Driver Code
    public static void main(String args[])
    {
        BinaryTree tree = new BinaryTree();
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
 
        /* Constructed binary tree is
             1
           /  \
          2    3
         / \  / \
        4   5 6  7 */
 
        int start = 2, end = 3;
 
        tree.printNodes(tree.root, start, end);
    }
}

Python3

# Python3 program for Print all nodes
# between two given levels in
# a binary tree
 
# Helper function that allocates a new
# node with the given data and None
# left and right pointers.                                
class newNode:
 
    # Construct to create a new node
    def __init__(self, key):
        self.data = key
        self.left = None
        self.right = None
 
# Iterative function to print all
# nodes between two given
# levels in a binary tree
def print Nodes(root, start, end):
     
    if (root == None):
        return
 
    # create an empty queue and
    # enqueue root node
    q = []
    q.append(root)
 
    # pointer to store current node
    curr = None
 
    # maintains level of current node
    level = 0
 
    # run till queue is not empty
    while (len(q)):
         
        # increment level by 1
        level += 1
 
        # calculate number of nodes in
        # current level
        size = len(q)
 
        # process every node of current level
        # and enqueue their non-empty left
        # and right child to queue
        while (size != 0) :
            curr = q[0]
            q.pop(0)
 
            # print the node if its level is
            # between given levels
            if (level >= start and level <= end) :
                print(curr.data, end = " ")
             
            if (curr.left != None) :
                q.append(curr.left)
             
            if (curr.right != None) :
                q.append(curr.right)
             
            size -= 1
         
        if (level >= start and level <= end) :
            print("")
             
# Driver Code
if __name__ == '__main__':
     
    """
    Let us create Binary Tree shown
    in above example """
    root = newNode(1)
    root.left = newNode(2)
 
    root.left.left = newNode(4)
    root.left.right = newNode(5)
    root.right = newNode(3)
    root.right.right = newNode(7)
    root.right.left = newNode(6)
    start = 2
    end = 3
    print Nodes(root, start, end)
     
# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

C#

// C# program for Print all nodes
// between two given levels in
// a binary tree
using System;
using System.Collections.Generic;
 
public class BinaryTree
{
 
    // Class containing left and right
    // child of current node and key value
    public class Node
    {
 
        public int data;
        public Node left, right;
 
        public Node(int item)
        {
            data = item;
            left = right = null;
        }
    }
 
    // Root of the Binary Tree
    Node root;
 
    public BinaryTree()
    {
        root = null;
    }
 
    // Iterative function to print all
    // nodes between two given
    // levels in a binary tree
    void printNodes(Node root, int start, int end)
    {
        if (root == null)
        {
            return;
        }
 
        // create an empty queue and
        // enqueue root node
        Queue queue = new Queue();
        queue.Enqueue(root);
 
        // pointer to store current node
        Node curr = null;
 
        // maintains level of current node
        int level = 0;
 
        // run till queue is not empty
        while (queue.Count >0)
        {
            // increment level by 1
            level++;
 
            // calculate number of nodes in
            // current level
            int size = queue.Count;
 
            // process every node of current level
            // and enqueue their non-empty left
            // and right child to queue
            while (size != 0)
            {
                curr = queue.Peek();
                queue.Dequeue();
 
                // print the node if its level is
                // between given levels
                if (level >= start && level <= end)
                {
                    Console.Write(curr.data + " ");
                }
                if (curr.left != null)
                {
                    queue.Enqueue(curr.left);
                }
 
                if (curr.right != null)
                {
                    queue.Enqueue(curr.right);
                }
                size--;
            }
 
            if (level >= start && level <= end)
            {
                Console.WriteLine("");
            };
        }
    }
 
    // Driver Code
    public static void Main(String []args)
    {
        BinaryTree tree = new BinaryTree();
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
 
        /* Constructed binary tree is
            1
        / \
        2 3
        / \ / \
        4 5 6 7 */
        int start = 2, end = 3;
 
        tree.printNodes(tree.root, start, end);
    }
}
 
// This code is contributed by 29AjayKumar

Javascript

    // Javascript program for Print all nodes
    // between two given levels in
    // a binary tree
     
    class Node
    {
        constructor(data) {
           this.left = null;
           this.right = null;
           this.data = data;
        }
    }
     
    // Root of the Binary Tree
    let root = null;
  
    // Iterative function to print all
    // nodes between two given
    // levels in a binary tree
    function printNodes(root, start, end)
    {
        if (root == null) {
            return;
        }
  
        // create an empty queue and
        // enqueue root node
        let queue = [];
        queue.push(root);
  
        // pointer to store current node
        let curr = null;
  
        // maintains level of current node
        let level = 0;
  
        // run till queue is not empty
        while (queue.length > 0) {
            // increment level by 1
            level++;
  
            // calculate number of nodes in
            // current level
            let size = queue.length;
  
            // process every node of current level
            // and enqueue their non-empty left
            // and right child to queue
            while (size != 0) {
                curr = queue[0];
                queue.shift();
  
                // print the node if its level is
                // between given levels
                if (level >= start && level <= end) {
                    document.write(curr.data + " ");
                }
                if (curr.left != null) {
                    queue.push(curr.left);
                }
  
                if (curr.right != null) {
                    queue.push(curr.right);
                }
                size--;
            }
  
            if (level >= start && level <= end) {
                document.write("</br>");
            }
        }
    }
     
    let tree = new Node(0);
    tree.root = new Node(1);
    tree.root.left = new Node(2);
    tree.root.right = new Node(3);
    tree.root.left.left = new Node(4);
    tree.root.left.right = new Node(5);
    tree.root.right.left = new Node(6);
    tree.root.right.right = new Node(7);
 
    /* Constructed binary tree is
               1
             /  \
            2    3
           / \  / \
          4   5 6  7 */
 
    let start = 2, end = 3;
 
    printNodes(tree.root, start, end);
  
 // This code is contributed by decode2207.

输出

2 3 
4 5 6 7