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feat: add solutions to lcp problem: No.67
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‎lcp/LCP 67. 装饰树/README.md‎

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<!-- 这里可写通用的实现逻辑 -->
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**方法一：递归**
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我们设计一个函数 $dfs(root)$，表示将灯饰插入以 $root$ 为根节点的树中，返回插入灯饰后的树的根节点。那么答案就是 $dfs(root)$。
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函数 $dfs(root)$ 的逻辑如下：
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- 若 $root$ 为空，则返回空；
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- 否则，递归地对 $root$ 的左右子树分别调用 $dfs$ 函数，得到插入灯饰后的左右子树的根节点 $l$ 和 $r$；
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- 若 $l$ 不为空，则我们创建一个新节点 $TreeNode(-1, l, null)$，并将其作为 $root$ 的左子节点；
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- 若 $r$ 不为空，则我们创建一个新节点 $TreeNode(-1, null, r)$，并将其作为 $root$ 的右子节点；
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最后，返回 $root$。
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时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 是树的节点数。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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class Solution:
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def expandBinaryTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
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def dfs(root):
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if root is None:
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return None
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l, r = dfs(root.left), dfs(root.right)
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if l:
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root.left = TreeNode(-1, l)
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if r:
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root.right = TreeNode(-1, None, r)
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return root
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return dfs(root)
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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/**
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode() {}
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* TreeNode(int val) { this.val = val; }
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* TreeNode(int val, TreeNode left, TreeNode right) {
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* this.val = val;
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* this.left = left;
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* this.right = right;
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* }
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* }
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*/
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class Solution {
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public TreeNode expandBinaryTree(TreeNode root) {
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return dfs(root);
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}
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private TreeNode dfs(TreeNode root) {
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if (root == null) {
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return null;
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}
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TreeNode l = dfs(root.left);
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TreeNode r = dfs(root.right);
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if (l != null) {
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root.left = new TreeNode(-1, l, null);
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}
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if (r != null) {
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root.right = new TreeNode(-1, null, r);
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}
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return root;
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}
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}
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```
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### **C++**
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```cpp
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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TreeNode* expandBinaryTree(TreeNode* root) {
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function<TreeNode*(TreeNode*)> dfs = [&](TreeNode* root) -> TreeNode* {
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if (!root) {
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return nullptr;
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}
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TreeNode* l = dfs(root->left);
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TreeNode* r = dfs(root->right);
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if (l) {
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root->left = new TreeNode(-1, l, nullptr);
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}
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if (r) {
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root->right = new TreeNode(-1, nullptr, r);
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}
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return root;
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};
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return dfs(root);
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}
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};
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```
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### **Go**
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```go
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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func expandBinaryTree(root *TreeNode) *TreeNode {
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var dfs func(*TreeNode) *TreeNode
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dfs = func(root *TreeNode) *TreeNode {
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if root == nil {
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return root
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}
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l, r := dfs(root.Left), dfs(root.Right)
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if l != nil {
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root.Left = &TreeNode{-1, l, nil}
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}
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if r != nil {
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root.Right = &TreeNode{-1, nil, r}
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}
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return root
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}
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return dfs(root)
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}
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```
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### **...**

‎lcp/LCP 67. 装饰树/Solution.cpp‎

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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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* };
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*/
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class Solution {
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public:
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TreeNode* expandBinaryTree(TreeNode* root) {
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function<TreeNode*(TreeNode*)> dfs = [&](TreeNode* root) -> TreeNode* {
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if (!root) {
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return nullptr;
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}
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TreeNode* l = dfs(root->left);
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TreeNode* r = dfs(root->right);
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if (l) {
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root->left = new TreeNode(-1, l, nullptr);
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}
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if (r) {
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root->right = new TreeNode(-1, nullptr, r);
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}
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return root;
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};
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return dfs(root);
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}
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};

‎lcp/LCP 67. 装饰树/Solution.go‎

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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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func expandBinaryTree(root *TreeNode) *TreeNode {
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var dfs func(*TreeNode) *TreeNode
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dfs = func(root *TreeNode) *TreeNode {
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if root == nil {
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return root
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}
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l, r := dfs(root.Left), dfs(root.Right)
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if l != nil {
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root.Left = &TreeNode{-1, l, nil}
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}
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if r != nil {
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root.Right = &TreeNode{-1, nil, r}
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}
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return root
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}
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return dfs(root)
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}

‎lcp/LCP 67. 装饰树/Solution.java‎

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/**
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode() {}
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* TreeNode(int val) { this.val = val; }
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* TreeNode(int val, TreeNode left, TreeNode right) {
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* this.val = val;
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* this.left = left;
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* this.right = right;
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* }
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* }
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*/
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class Solution {
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public TreeNode expandBinaryTree(TreeNode root) {
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return dfs(root);
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}
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private TreeNode dfs(TreeNode root) {
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if (root == null) {
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return null;
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}
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TreeNode l = dfs(root.left);
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TreeNode r = dfs(root.right);
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if (l != null) {
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root.left = new TreeNode(-1, l, null);
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}
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if (r != null) {
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root.right = new TreeNode(-1, null, r);
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}
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return root;
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}
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}

‎lcp/LCP 67. 装饰树/Solution.py‎

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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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class Solution:
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def expandBinaryTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
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def dfs(root):
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if root is None:
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return None
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l, r = dfs(root.left), dfs(root.right)
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if l:
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root.left = TreeNode(-1, l)
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if r:
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root.right = TreeNode(-1, None, r)
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return root
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return dfs(root)

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