feat(csharp): add csharp code for array binary tree (#632)
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codes/csharp/chapter_tree/array_binary_tree.cs
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134
codes/csharp/chapter_tree/array_binary_tree.cs
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/**
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* File: array_binary_tree.cs
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* Created Time: 2023-07-20
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* Author: hpstory (hpstory1024@163.com)
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*/
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namespace hello_algo.chapter_tree;
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/* 数组表示下的二叉树类 */
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public class ArrayBinaryTree {
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private List<int?> tree;
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/* 构造方法 */
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public ArrayBinaryTree(List<int?> arr) {
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tree = new List<int?>(arr);
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}
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/* 节点数量 */
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public int size() {
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return tree.Count;
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}
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/* 获取索引为 i 节点的值 */
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public int? val(int i) {
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// 若索引越界，则返回 null ，代表空位
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if (i < 0 || i >= size())
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return null;
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return tree[i];
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}
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/* 获取索引为 i 节点的左子节点的索引 */
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public int left(int i) {
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return 2 * i + 1;
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}
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/* 获取索引为 i 节点的右子节点的索引 */
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public int right(int i) {
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return 2 * i + 2;
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}
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/* 获取索引为 i 节点的父节点的索引 */
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public int parent(int i) {
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return (i - 1) / 2;
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}
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/* 层序遍历 */
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public List<int> levelOrder() {
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List<int> res = new List<int>();
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// 直接遍历数组
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for (int i = 0; i < size(); i++) {
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if (val(i).HasValue)
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res.Add(val(i).Value);
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}
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return res;
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}
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/* 深度优先遍历 */
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private void dfs(int i, string order, List<int> res) {
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// 若为空位，则返回
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if (!val(i).HasValue)
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return;
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// 前序遍历
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if (order == "pre")
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res.Add(val(i).Value);
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dfs(left(i), order, res);
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// 中序遍历
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if (order == "in")
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res.Add(val(i).Value);
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dfs(right(i), order, res);
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// 后序遍历
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if (order == "post")
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res.Add(val(i).Value);
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}
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/* 前序遍历 */
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public List<int> preOrder() {
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List<int> res = new List<int>();
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dfs(0, "pre", res);
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return res;
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}
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/* 中序遍历 */
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public List<int> inOrder() {
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List<int> res = new List<int>();
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dfs(0, "in", res);
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return res;
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}
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/* 后序遍历 */
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public List<int> postOrder() {
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List<int> res = new List<int>();
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dfs(0, "post", res);
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return res;
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}
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}
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public class array_binary_tree {
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[Test]
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public void Test() {
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// 初始化二叉树
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// 这里借助了一个从数组直接生成二叉树的函数
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List<int?> arr = new List<int?> { 1, 2, 3, 4, null, 6, 7, 8, 9, null, null, 12, null, null, 15 };
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TreeNode root = TreeNode.ListToTree(arr);
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Console.WriteLine("\n初始化二叉树\n");
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Console.WriteLine("二叉树的数组表示：");
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Console.WriteLine(arr.PrintList());
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Console.WriteLine("二叉树的链表表示：");
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PrintUtil.PrintTree(root);
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// 数组表示下的二叉树类
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ArrayBinaryTree abt = new ArrayBinaryTree(arr);
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// 访问节点
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int i = 1;
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int l = abt.left(i);
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int r = abt.right(i);
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int p = abt.parent(i);
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Console.WriteLine("\n当前节点的索引为 " + i + " ，值为 " + abt.val(i));
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Console.WriteLine("其左子节点的索引为 " + l + " ，值为 " + (abt.val(l).HasValue ? abt.val(l) : "null"));
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Console.WriteLine("其右子节点的索引为 " + r + " ，值为 " + (abt.val(r).HasValue ? abt.val(r) : "null"));
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Console.WriteLine("其父节点的索引为 " + p + " ，值为 " + (abt.val(p).HasValue ? abt.val(p) : "null"));
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// 遍历树
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List<int> res = abt.levelOrder();
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Console.WriteLine("\n层序遍历为：" + res.PrintList());
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res = abt.preOrder();
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Console.WriteLine("前序遍历为：" + res.PrintList());
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res = abt.inOrder();
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Console.WriteLine("中序遍历为：" + res.PrintList());
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res = abt.postOrder();
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Console.WriteLine("后序遍历为：" + res.PrintList());
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}
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}
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@ -16,12 +16,16 @@ public class Trunk {
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}
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};
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public class PrintUtil {
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public static class PrintUtil {
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/* Print a list */
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public static void PrintList<T>(IList<T> list) {
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Console.WriteLine("[" + string.Join(", ", list) + "]");
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}
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public static string PrintList<T>(this IEnumerable<T?> list) {
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return $"[ {string.Join(", ", list.Select(x => x?.ToString() ?? "null"))} ]";
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}
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/* Print a matrix (Array) */
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public static void PrintMatrix<T>(T[][] matrix) {
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Console.WriteLine("[");
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@ -131,4 +135,4 @@ public class PrintUtil {
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TreeNode tree = TreeNode.ListToTree(list.Cast<int?>().ToList());
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PrintTree(tree);
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}
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}
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}
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@ -13,50 +13,59 @@ public class TreeNode {
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public TreeNode? left; // 左子节点引用
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public TreeNode? right; // 右子节点引用
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/* 构造方法 */
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public TreeNode(int x) {
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val = x;
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}
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/* Generate a binary tree given an array */
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public static TreeNode? ListToTree(List<int?> arr) {
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if (arr.Count == 0 || arr[0] == null)
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return null;
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// 序列化编码规则请参考：
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// https://www.hello-algo.com/chapter_tree/array_representation_of_tree/
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// 二叉树的数组表示：
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// [1, 2, 3, 4, None, 6, 7, 8, 9, None, None, 12, None, None, 15]
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// 二叉树的链表表示：
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// /——— 15
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// /——— 7
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// /——— 3
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// | \——— 6
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// | \——— 12
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// ——— 1
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// \——— 2
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// | /——— 9
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// \——— 4
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// \——— 8
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TreeNode root = new TreeNode(arr[0]!.Value);
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Queue<TreeNode> queue = new Queue<TreeNode>();
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queue.Enqueue(root);
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int i = 0;
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while (queue.Count != 0) {
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TreeNode node = queue.Dequeue();
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if (++i >= arr.Count) break;
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if (arr[i] != null) {
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node.left = new TreeNode((int)arr[i]);
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queue.Enqueue(node.left);
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}
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if (++i >= arr.Count) break;
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if (arr[i] != null) {
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node.right = new TreeNode((int)arr[i]);
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queue.Enqueue(node.right);
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}
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/* 将列表反序列化为二叉树：递归 */
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private static TreeNode? ListToTreeDFS(List<int?> arr, int i) {
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if (i < 0|| i >= arr.Count || !arr[i].HasValue) {
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return null;
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}
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TreeNode root = new TreeNode(arr[i].Value);
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root.left = ListToTreeDFS(arr, 2 * i + 1);
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root.right = ListToTreeDFS(arr, 2 * i + 2);
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return root;
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}
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/* Serialize a binary tree to a list */
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public static List<int?> TreeToList(TreeNode root) {
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List<int?> list = new();
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if (root == null) return list;
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Queue<TreeNode?> queue = new();
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while (queue.Count != 0) {
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TreeNode? node = queue.Dequeue();
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if (node != null) {
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list.Add(node.val);
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queue.Enqueue(node.left);
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queue.Enqueue(node.right);
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} else {
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list.Add(null);
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}
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/* 将列表反序列化为二叉树 */
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public static TreeNode? ListToTree(List<int?> arr) {
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return ListToTreeDFS(arr, 0);
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}
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/* 将二叉树序列化为列表：递归 */
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private static void TreeToListDFS(TreeNode? root, int i, List<int?> res) {
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if (root == null)
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return;
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while (i >= res.Count) {
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res.Add(null);
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}
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return list;
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res[i] = root.val;
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TreeToListDFS(root.left, 2 * i + 1, res);
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TreeToListDFS(root.right, 2 * i + 2, res);
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}
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/* 将二叉树序列化为列表 */
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public static List<int?> treeToList(TreeNode root) {
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List<int?> res = new List<int?>();
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TreeToListDFS(root, 0, res);
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return res;
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}
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}
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