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feat(csharp): add csharp code for array binary tree #632

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merged 1 commit into from Jul 20, 2023
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feat(csharp): add csharp code for array binary tree #632

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134 changes: 134 additions & 0 deletions codes/csharp/chapter_tree/array_binary_tree.cs
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@@ -0,0 +1,134 @@
/**
* File: array_binary_tree.cs
* Created Time: 2023-07-20
* Author: hpstory (hpstory1024@163.com)
*/

namespace hello_algo.chapter_tree;

/* 数组表示下的二叉树类 */
public class ArrayBinaryTree {
private List<int?> tree;

/* 构造方法 */
public ArrayBinaryTree(List<int?> arr) {
tree = new List<int?>(arr);
}

/* 节点数量 */
public int size() {
return tree.Count;
}

/* 获取索引为 i 节点的值 */
public int? val(int i) {
// 若索引越界，则返回 null ，代表空位
if (i < 0 || i >= size())
return null;
return tree[i];
}

/* 获取索引为 i 节点的左子节点的索引 */
public int left(int i) {
return 2 * i + 1;
}

/* 获取索引为 i 节点的右子节点的索引 */
public int right(int i) {
return 2 * i + 2;
}

/* 获取索引为 i 节点的父节点的索引 */
public int parent(int i) {
return (i - 1) / 2;
}

/* 层序遍历 */
public List<int> levelOrder() {
List<int> res = new List<int>();
// 直接遍历数组
for (int i = 0; i < size(); i++) {
if (val(i).HasValue)
res.Add(val(i).Value);
}
return res;
}

/* 深度优先遍历 */
private void dfs(int i, string order, List<int> res) {
// 若为空位，则返回
if (!val(i).HasValue)
return;
// 前序遍历
if (order == "pre")
res.Add(val(i).Value);
dfs(left(i), order, res);
// 中序遍历
if (order == "in")
res.Add(val(i).Value);
dfs(right(i), order, res);
// 后序遍历
if (order == "post")
res.Add(val(i).Value);
}

/* 前序遍历 */
public List<int> preOrder() {
List<int> res = new List<int>();
dfs(0, "pre", res);
return res;
}

/* 中序遍历 */
public List<int> inOrder() {
List<int> res = new List<int>();
dfs(0, "in", res);
return res;
}

/* 后序遍历 */
public List<int> postOrder() {
List<int> res = new List<int>();
dfs(0, "post", res);
return res;
}
}

public class array_binary_tree {
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This part of code is different with others. Because ArrayBinaryTree class doesn't have a default constructor for test framework, resulting in a test failure, so move it outside of the class.

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I see. C#'s rule is the same with Java.

[Test]
public void Test() {
// 初始化二叉树
// 这里借助了一个从数组直接生成二叉树的函数
List<int?> arr = new List<int?> { 1, 2, 3, 4, null, 6, 7, 8, 9, null, null, 12, null, null, 15 };

TreeNode root = TreeNode.ListToTree(arr);
Console.WriteLine("\n初始化二叉树\n");
Console.WriteLine("二叉树的数组表示：");
Console.WriteLine(arr.PrintList());
Console.WriteLine("二叉树的链表表示：");
PrintUtil.PrintTree(root);

// 数组表示下的二叉树类
ArrayBinaryTree abt = new ArrayBinaryTree(arr);

// 访问节点
int i = 1;
int l = abt.left(i);
int r = abt.right(i);
int p = abt.parent(i);
Console.WriteLine("\n当前节点的索引为 " + i + " ，值为 " + abt.val(i));
Console.WriteLine("其左子节点的索引为 " + l + " ，值为 " + (abt.val(l).HasValue ? abt.val(l) : "null"));
Console.WriteLine("其右子节点的索引为 " + r + " ，值为 " + (abt.val(r).HasValue ? abt.val(r) : "null"));
Console.WriteLine("其父节点的索引为 " + p + " ，值为 " + (abt.val(p).HasValue ? abt.val(p) : "null"));

// 遍历树
List<int> res = abt.levelOrder();
Console.WriteLine("\n层序遍历为：" + res.PrintList());
res = abt.preOrder();
Console.WriteLine("前序遍历为：" + res.PrintList());
res = abt.inOrder();
Console.WriteLine("中序遍历为：" + res.PrintList());
res = abt.postOrder();
Console.WriteLine("后序遍历为：" + res.PrintList());
}
}
8 changes: 6 additions & 2 deletions codes/csharp/utils/PrintUtil.cs
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Expand Up @@ -16,12 +16,16 @@ public class Trunk {
}
};

public class PrintUtil {
public static class PrintUtil {
/* Print a list */
public static void PrintList<T>(IList<T> list) {
Console.WriteLine("[" + string.Join(", ", list) + "]");
}

public static string PrintList<T>(this IEnumerable<T?> list) {
return $"[ {string.Join(", ", list.Select(x => x?.ToString() ?? "null"))} ]";
}

/* Print a matrix (Array) */
public static void PrintMatrix<T>(T[][] matrix) {
Console.WriteLine("[");
Expand Down Expand Up @@ -131,4 +135,4 @@ public class PrintUtil {
TreeNode tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
PrintTree(tree);
}
}
}
79 changes: 44 additions & 35 deletions codes/csharp/utils/TreeNode.cs
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Expand Up @@ -13,50 +13,59 @@ public class TreeNode {
public TreeNode? left; // 左子节点引用
public TreeNode? right; // 右子节点引用

/* 构造方法 */
public TreeNode(int x) {
val = x;
}

/* Generate a binary tree given an array */
public static TreeNode? ListToTree(List<int?> arr) {
if (arr.Count == 0 || arr[0] == null)
return null;
// 序列化编码规则请参考：
// https://www.hello-algo.com/chapter_tree/array_representation_of_tree/
// 二叉树的数组表示：
// [1, 2, 3, 4, None, 6, 7, 8, 9, None, None, 12, None, None, 15]
// 二叉树的链表表示：
// /——— 15
// /——— 7
// /——— 3
// | \——— 6
// | \——— 12
// ——— 1
// \——— 2
// | /——— 9
// \——— 4
// \——— 8

TreeNode root = new TreeNode(arr[0]!.Value);
Queue<TreeNode> queue = new Queue<TreeNode>();
queue.Enqueue(root);
int i = 0;
while (queue.Count != 0) {
TreeNode node = queue.Dequeue();
if (++i >= arr.Count) break;
if (arr[i] != null) {
node.left = new TreeNode((int)arr[i]);
queue.Enqueue(node.left);
}
if (++i >= arr.Count) break;
if (arr[i] != null) {
node.right = new TreeNode((int)arr[i]);
queue.Enqueue(node.right);
}
/* 将列表反序列化为二叉树：递归 */
private static TreeNode? ListToTreeDFS(List<int?> arr, int i) {
if (i < 0|| i >= arr.Count || !arr[i].HasValue) {
return null;
}
TreeNode root = new TreeNode(arr[i].Value);
root.left = ListToTreeDFS(arr, 2 * i + 1);
root.right = ListToTreeDFS(arr, 2 * i + 2);
return root;
}

/* Serialize a binary tree to a list */
public static List<int?> TreeToList(TreeNode root) {
List<int?> list = new();
if (root == null) return list;
Queue<TreeNode?> queue = new();
while (queue.Count != 0) {
TreeNode? node = queue.Dequeue();
if (node != null) {
list.Add(node.val);
queue.Enqueue(node.left);
queue.Enqueue(node.right);
} else {
list.Add(null);
}
/* 将列表反序列化为二叉树 */
public static TreeNode? ListToTree(List<int?> arr) {
return ListToTreeDFS(arr, 0);
}

/* 将二叉树序列化为列表：递归 */
private static void TreeToListDFS(TreeNode? root, int i, List<int?> res) {
if (root == null)
return;
while (i >= res.Count) {
res.Add(null);
}
return list;
res[i] = root.val;
TreeToListDFS(root.left, 2 * i + 1, res);
TreeToListDFS(root.right, 2 * i + 2, res);
}

/* 将二叉树序列化为列表 */
public static List<int?> treeToList(TreeNode root) {
List<int?> res = new List<int?>();
TreeToListDFS(root, 0, res);
return res;
}
}