feat: add solutions to lc problem: No.0431 (#3602)

No.0431.Encode N-ary Tree to Binary Tree

Author: yanglbme

solution/0400-0499/0431.Encode N-ary Tree to Binary Tree/README.md

@@ -76,32 +76,363 @@ tags:
 
 <!-- solution:start -->
 
-### 方法一
+### 方法一：递归
+
+我们可以将二叉树的左指针指向 N 叉树的第一个孩子，将二叉树的右指针指向 N 叉树的下一个兄弟节点。
+
+时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 为 N 叉树的节点数量。
 
 <!-- tabs:start -->
 
 #### Python3
 
 ```python
-
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, val: Optional[int] = None, children: Optional[List['Node']] = None):
+        self.val = val
+        self.children = children
+"""
+
+"""
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+"""
+
+
+class Codec:
+    # Encodes an n-ary tree to a binary tree.
+    def encode(self, root: "Optional[Node]") -> Optional[TreeNode]:
+        if root is None:
+            return None
+        node = TreeNode(root.val)
+        if not root.children:
+            return node
+        left = self.encode(root.children[0])
+        node.left = left
+        for child in root.children[1:]:
+            left.right = self.encode(child)
+            left = left.right
+        return node
+
+    # Decodes your binary tree to an n-ary tree.
+    def decode(self, data: Optional[TreeNode]) -> "Optional[Node]":
+        if data is None:
+            return None
+        node = Node(data.val, [])
+        if data.left is None:
+            return node
+        left = data.left
+        while left:
+            node.children.append(self.decode(left))
+            left = left.right
+        return node
+
+
+# Your Codec object will be instantiated and called as such:
+# codec = Codec()
+# codec.decode(codec.encode(root))
 ```
 
 #### Java
 
 ```java
-
+/*
+// Definition for a Node.
+class Node {
+    public int val;
+    public List<Node> children;
+
+    public Node() {}
+
+    public Node(int _val) {
+        val = _val;
+    }
+
+    public Node(int _val, List<Node> _children) {
+        val = _val;
+        children = _children;
+    }
+};
+*/
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+
+class Codec {
+    // Encodes an n-ary tree to a binary tree.
+    public TreeNode encode(Node root) {
+        if (root == null) {
+            return null;
+        }
+        TreeNode node = new TreeNode(root.val);
+        if (root.children == null || root.children.isEmpty()) {
+            return node;
+        }
+        TreeNode left = encode(root.children.get(0));
+        node.left = left;
+        for (int i = 1; i < root.children.size(); i++) {
+            left.right = encode(root.children.get(i));
+            left = left.right;
+        }
+        return node;
+    }
+
+    // Decodes your binary tree to an n-ary tree.
+    public Node decode(TreeNode data) {
+        if (data == null) {
+            return null;
+        }
+        Node node = new Node(data.val, new ArrayList<>());
+        if (data.left == null) {
+            return node;
+        }
+        TreeNode left = data.left;
+        while (left != null) {
+            node.children.add(decode(left));
+            left = left.right;
+        }
+        return node;
+    }
+}
+
+// Your Codec object will be instantiated and called as such:
+// Codec codec = new Codec();
+// codec.decode(codec.encode(root));
 ```
 
 #### C++
 
 ```cpp
-
+/*
+// Definition for a Node.
+class Node {
+public:
+    int val;
+    vector<Node*> children;
+
+    Node() {}
+
+    Node(int _val) {
+        val = _val;
+    }
+
+    Node(int _val, vector<Node*> _children) {
+        val = _val;
+        children = _children;
+    }
+};
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Codec {
+public:
+    // Encodes an n-ary tree to a binary tree.
+    TreeNode* encode(Node* root) {
+        if (root == nullptr) {
+            return nullptr;
+        }
+        TreeNode* node = new TreeNode(root->val);
+        if (root->children.empty()) {
+            return node;
+        }
+        TreeNode* left = encode(root->children[0]);
+        node->left = left;
+        for (int i = 1; i < root->children.size(); i++) {
+            left->right = encode(root->children[i]);
+            left = left->right;
+        }
+        return node;
+    }
+
+    // Decodes your binary tree to an n-ary tree.
+    Node* decode(TreeNode* data) {
+        if (data == nullptr) {
+            return nullptr;
+        }
+        Node* node = new Node(data->val, vector<Node*>());
+        if (data->left == nullptr) {
+            return node;
+        }
+        TreeNode* left = data->left;
+        while (left != nullptr) {
+            node->children.push_back(decode(left));
+            left = left->right;
+        }
+        return node;
+    }
+};
+
+// Your Codec object will be instantiated and called as such:
+// Codec codec;
+// codec.decode(codec.encode(root));
 ```
 
 #### Go
 
 ```go
+/**
+ * Definition for a Node.
+ * type Node struct {
+ *     Val int
+ *     Children []*Node
+ * }
+ */
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+type Codec struct {
+}
+
+func Constructor() *Codec {
+	return &Codec{}
+}
+
+// Encodes an n-ary tree to a binary tree.
+func (this *Codec) encode(root *Node) *TreeNode {
+	if root == nil {
+		return nil
+	}
+	node := &TreeNode{Val: root.Val}
+	if len(root.Children) == 0 {
+		return node
+	}
+	left := this.encode(root.Children[0])
+	node.Left = left
+	for i := 1; i < len(root.Children); i++ {
+		left.Right = this.encode(root.Children[i])
+		left = left.Right
+	}
+	return node
+}
+
+// Decodes your binary tree to an n-ary tree.
+func (this *Codec) decode(data *TreeNode) *Node {
+	if data == nil {
+		return nil
+	}
+	node := &Node{Val: data.Val, Children: []*Node{}}
+	if data.Left == nil {
+		return node
+	}
+	left := data.Left
+	for left != nil {
+		node.Children = append(node.Children, this.decode(left))
+		left = left.Right
+	}
+	return node
+}
+
+/**
+ * Your Codec object will be instantiated and called as such:
+ * obj := Constructor();
+ * bst := obj.encode(root);
+ * ans := obj.decode(bst);
+ */
+```
 
+#### TypeScript
+
+```ts
+/**
+ * Definition for _Node.
+ * class _Node {
+ *     val: number
+ *     children: _Node[]
+ *
+ *     constructor(v: number) {
+ *         this.val = v;
+ *         this.children = [];
+ *     }
+ * }
+ */
+
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+class Codec {
+    constructor() {}
+
+    // Encodes an n-ary tree to a binary tree.
+    serialize(root: _Node | null): TreeNode | null {
+        if (root === null) {
+            return null;
+        }
+        const node = new TreeNode(root.val);
+        if (root.children.length === 0) {
+            return node;
+        }
+        let left: TreeNode | null = this.serialize(root.children[0]);
+        node.left = left;
+        for (let i = 1; i < root.children.length; i++) {
+            if (left) {
+                left.right = this.serialize(root.children[i]);
+                left = left.right;
+            }
+        }
+        return node;
+    }
+
+    // Decodes your binary tree back to an n-ary tree.
+    deserialize(root: TreeNode | null): _Node | null {
+        if (root === null) {
+            return null;
+        }
+        const node = new _Node(root.val);
+        if (root.left === null) {
+            return node;
+        }
+        let left: TreeNode | null = root.left;
+        while (left !== null) {
+            node.children.push(this.deserialize(left));
+            left = left.right;
+        }
+        return node;
+    }
+}
+
+// Your Codec object will be instantiated and called as such:
+// Codec codec = new Codec();
+// codec.deserialize(codec.serialize(root));
 ```
 
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