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chapter_divide_and_conquer/build_binary_tree_problem.md
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@@ -2,7 +2,7 @@
comments: true
---
# 12.2.   构建二叉树问题
# 12.3.   构建二叉树问题
!!! question
@@ -64,17 +64,65 @@ comments: true
=== "Java"
```java title="build_tree.java"
[class]{build_tree}-[func]{dfs}
/* 构建二叉树：分治 */
TreeNode dfs(int[] preorder, int[] inorder, Map<Integer, Integer> hmap, int i, int l, int r) {
// 子树区间为空时终止
if (r - l < 0)
return null;
// 初始化根节点
TreeNode root = new TreeNode(preorder[i]);
// 查询 m ，从而划分左右子树
int m = hmap.get(preorder[i]);
// 子问题：构建左子树
root.left = dfs(preorder, inorder, hmap, i + 1, l, m - 1);
// 子问题：构建右子树
root.right = dfs(preorder, inorder, hmap, i + 1 + m - l, m + 1, r);
// 返回根节点
return root;
}
[class]{build_tree}-[func]{buildTree}
/* 构建二叉树 */
TreeNode buildTree(int[] preorder, int[] inorder) {
// 初始化哈希表，存储 inorder 元素到索引的映射
Map<Integer, Integer> hmap = new HashMap<>();
for (int i = 0; i < inorder.length; i++) {
hmap.put(inorder[i], i);
}
TreeNode root = dfs(preorder, inorder, hmap, 0, 0, inorder.length - 1);
return root;
}
```
=== "C++"
```cpp title="build_tree.cpp"
[class]{}-[func]{dfs}
/* 构建二叉树：分治 */
TreeNode *dfs(vector<int> &preorder, vector<int> &inorder, unordered_map<int, int> &hmap, int i, int l, int r) {
// 子树区间为空时终止
if (r - l < 0)
return NULL;
// 初始化根节点
TreeNode *root = new TreeNode(preorder[i]);
// 查询 m ，从而划分左右子树
int m = hmap[preorder[i]];
// 子问题：构建左子树
root->left = dfs(preorder, inorder, hmap, i + 1, l, m - 1);
// 子问题：构建右子树
root->right = dfs(preorder, inorder, hmap, i + 1 + m - l, m + 1, r);
// 返回根节点
return root;
}
[class]{}-[func]{buildTree}
/* 构建二叉树 */
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
// 初始化哈希表，存储 inorder 元素到索引的映射
unordered_map<int, int> hmap;
for (int i = 0; i < inorder.size(); i++) {
hmap[inorder[i]] = i;
}
TreeNode *root = dfs(preorder, inorder, hmap, 0, 0, inorder.size() - 1);
return root;
}
```
=== "Python"