【算法】根据二叉树的级别返回排序后的元素列表

算法,根据,二叉树,级别,返回,排序,元素,列表 · 浏览次数 : 4

小编点评

```csharp public class Node { public Node Left; public Node Right; public int Value; public Node(Node l, Node r, int v) { Left = l; Right = r; Value = v; } } public class Kata { public static List TreeByLevels(Node root) { List result = new List(); Queue queue = new Queue(); queue.Enqueue(root); while (queue.Count > 0) { Node node = queue.Dequeue(); result.Add(node.Value); if (node.Left != null) queue.Enqueue(node.Left); if (node.Right != null) queue.Enqueue(node.Right); } return result; } } ``` **测试用例：** ```csharp // 单个节点 [Test] public void SingleNodeTest() { Assert.AreEqual(new List() { 1 }, Kata.TreeByLevels(new Node(null, null, 1))); } // 左倾斜树 [Test] public void LeftSkewedTreeTest() { Assert.AreEqual(new List() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(new Node(null, null, 4), null, 2), null, 1)); } // 右倾斜树 [Test] public void RightSkewedTreeTest() { Assert.AreEqual(new List() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(null, new Node(null, new Node(null, null, 5), 3), 1)); } // 完全二叉树 [Test] public void CompleteBinaryTreeTest() { Assert.AreEqual(new List() { 1, 2, 3, 4, 5, 6, 7, 8, 9 }, Kata.TreeByLevels(new Node(23, new Node(new Node(null, null, 4), new Node(null, null, 5), 2), 24, new Node(new Node(null, null, 6), new Node(null, null, 7), 3), 25, 1))); } // 空节点 [Test] public void SkewedTreeWithNullNodesTest() { Assert.AreEqual(new List() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(32, null, null, 2), 33, null, 34, 1)); } ```

正文

根据给定的Node树节点，返回包含按级别排序的树中元素的列表，这意味着根元素位于第一位，然后根子元素（从左到右）位于第二位和第三位，依此类推。

 1 public class Node
 2 {
 3     public Node Left;
 4     public Node Right;
 5     public int Value;
 6     
 7     public Node(Node l, Node r, int v)
 8     {
 9         Left = l;
10         Right = r;
11         Value = v;
12     }
13 }
14 
15 示例1 :
16 
17                  2
18             8        9
19           1  3     4   5
20 需要返回list:
21 
22 [2,8,9,1,3,4,5]
23 示例2 :
24 
25                  1
26             8        4
27               3        5
28                          7
29 需要返回list:
30 
31 [1,8,4,3,5,7]

算法实现：

 1 using System;
 2 using System.Collections.Generic;
 3 
 4 public class Kata
 5 {
 6     public static List<int> TreeByLevels(Node root)
 7     {
 8         List<int> result = new List<int>();
 9 
10         if (root == null)
11             return result;
12 
13         Queue<Node> queue = new Queue<Node>();
14         queue.Enqueue(root);
15 
16         while (queue.Count > 0)
17         {
18             Node node = queue.Dequeue();
19             result.Add(node.Value);
20 
21             if (node.Left != null)
22                 queue.Enqueue(node.Left);
23             if (node.Right != null)
24                 queue.Enqueue(node.Right);
25         }
26 
27         return result;
28     }
29 }

测试用例：

 1 [Test]
 2 public void SingleNodeTest()
 3 {
 4     Assert.AreEqual(new List<int>() { 1 }, Kata.TreeByLevels(new Node(null, null, 1)));
 5 }
 6 
 7 [Test]
 8 public void LeftSkewedTreeTest()
 9 {
10     Assert.AreEqual(new List<int>() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(new Node(new Node(null, null, 4), null, 2), null, 1)));
11 }
12 
13 [Test]
14 public void RightSkewedTreeTest()
15 {
16     Assert.AreEqual(new List<int>() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(null, new Node(null, new Node(null, null, 5), 3), 1)));
17 }
18 
19 [Test]
20 public void CompleteBinaryTreeTest()
21 {
22     Assert.AreEqual(new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9 }, Kata.TreeByLevels(new Node(
23         new Node(new Node(null, null, 4), new Node(null, null, 5), 2),
24         new Node(new Node(null, null, 6), new Node(null, null, 7), 3),
25         1)));
26 }
27 
28 [Test]
29 public void SkewedTreeWithNullNodesTest()
30 {
31     Assert.AreEqual(new List<int>() { 1, 2, 3, 4, 5 }, Kata.TreeByLevels(new Node(
32         new Node(null, null, 2),
33         null,
34         1)));
35 }
36 
37 /*这些测试用例覆盖了一些特殊情况，包括：
38 
39 - 单个节点的情况；
40 - 左倾斜的树（即只有左子树的树）的情况；
41 - 右倾斜的树（即只有右子树的树）的情况；
42 - 完全二叉树的情况；
43 - 包含空节点（null）的树的情况。
44 
45 通过这些测试用例，可以验证算法在各种情况下的正确性和鲁棒性。*/