广度优先遍历 [英] Breadth-first traversal

问题描述

我试图解决一个面试问题，但为此我必须逐级遍历二叉树。我设计的BinaryNode具有以下变量

I was trying to solve one interview question, but for that I have to travel the binary tree level by level. I have designed BinaryNode with having below variable

private object data;
private BinaryNode left;
private BinaryNode right;

有人可以帮我在BinarySearchTree类中编写BreadthFirstSearch方法吗？

Could someone please help to write the BreadthFirstSearch method inside my BinarySearchTree class?

更新：谢谢大家的投入。这就是面试的问题。
给出一个二叉搜索树，设计一种算法，该算法创建每个深度的所有节点的链表（即，如果您的树的深度为D，则将有D个链表）。

Update: Thanks everyone for your inputs. So this was the interview question. "Given a binary search tree, design an algorithm which creates a linked list of all the nodes at each depth (i.e., if you have a tree with depth D, you’ll have D linked lists)".

这是我的方法，请告诉我您的专家意见。

Here is my Method, let me know your expert comment.

public List<LinkedList<BNode>> FindLevelLinkList(BNode root)
    {
        Queue<BNode> q = new Queue<BNode>();
        // List of all nodes starting from root.
        List<BNode> list = new List<BNode>();
        q.Enqueue(root);
        while (q.Count > 0)
        {
            BNode current = q.Dequeue();
            if (current == null)
                continue;
            q.Enqueue(current.Left);
            q.Enqueue(current.Right);
            list.Add(current);
        }

        // Add tree nodes of same depth into individual LinkedList. Then add all LinkedList into a List
        LinkedList<BNode> LL = new LinkedList<BNode>();
        List<LinkedList<BNode>> result = new List<LinkedList<BNode>>();
        LL.AddLast(root);
        int currentDepth = 0;
        foreach (BNode node in list)
        {
           if (node != root)
            {
                if (node.Depth == currentDepth)
                {
                    LL.AddLast(node);
                }
                else
                {
                    result.Add(LL);
                    LL = new LinkedList<BNode>();
                    LL.AddLast(node);
                    currentDepth++;
                }
            }
        }

        // Add the last linkedlist
        result.Add(LL);
        return result;
    }

推荐答案

通常是广度优先搜索

Queue<Node> q = new Queue<Node>();
q.Enqueue(root);
while(q.Count > 0)
{
    Node current = q.Dequeue();
    if(current == null)
        continue;
    q.Enqueue(current.Left);
    q.Enqueue(current.Right);

    DoSomething(current);
}

作为检查 null 出队后，您可以在添加到队列之前进行检查。我没有编译代码，所以它可能包含一些小错误。

As an alternative to checking for null after dequeuing you can check before adding to the Queue. I didn't compile the code, so it might contain some small mistakes.

一个更好（但速度较慢）的版本与LINQ很好地集成：

A fancier (but slower) version that integrates well with LINQ:

public static IEnumerable<T> BreadthFirstTopDownTraversal<T>(T root, Func<T, IEnumerable<T>> children)
{
    var q = new Queue<T>();
    q.Enqueue(root);
    while (q.Count > 0)
    {
        T current = q.Dequeue();
        yield return current;
        foreach (var child in children(current))
            q.Enqueue(child);
    }
}

可以与<$ c $一起使用c> 节点上的儿童属性：

Which can be used together with a Children property on Node:

IEnumerable<Node> Children { get { return new []{ Left, Right }.Where(x => x != null); } }

...

foreach(var node in BreadthFirstTopDownTraversal(root, node => node.Children))
{
   ...
}

这篇关于广度优先遍历的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！