s0669

include/s0669_trim_a_binary_search_tree.hpp

@@ -0,0 +1,11 @@
+#ifndef S0669_TRIM_A_BINARY_SEARCH_TREE_HPP
+#define S0669_TRIM_A_BINARY_SEARCH_TREE_HPP
+
+#include "structures.hpp"
+
+class S0669 {
+ public:
+  TreeNode* trimBST(TreeNode* root, int low, int high);
+};
+
+#endif

notes/src/bstree.md

@@ -3,3 +3,4 @@
 - [s0235](https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-search-tree/description/): 找两个指定节点的最近公共祖先。思路很简单，只要出现分岔（即一个在当前节点的左边，一个在当前节点的右边），那么这个分岔点就是最近公共祖先。
 - [s0701](https://leetcode.cn/problems/insert-into-a-binary-search-tree/description/): 插入节点。一层一层往下找，直到发现找不到了就在这个地方插入。
 - [s0450](https://leetcode.cn/problems/delete-node-in-a-bst/description/): 删除节点。递归删除。
+- [s0669](https://leetcode.cn/problems/trim-a-binary-search-tree/description/): 修剪 BST 。递归修剪。

src/s0669_trim_a_binary_search_tree.cpp

@@ -0,0 +1,17 @@
+#include "s0669_trim_a_binary_search_tree.hpp"
+
+TreeNode* S0669::trimBST(TreeNode* root, int low, int high) {
+  if (root == nullptr) return nullptr;
+  if (low <= root->val && root->val <= high) {
+    // 如果根节点的值位于范围内，则对左右子树进行剪裁
+    root->left = trimBST(root->left, low, high);
+    root->right = trimBST(root->right, low, high);
+    return root;
+  } else if (root->val < low) {
+    // 如果根节点的值小于 low, 把根节点和左子树都剪裁掉
+    return trimBST(root->right, low, high);
+  } else {
+    // 如果根节点的值大于 high, 把根节点和右子树都剪裁掉
+    return trimBST(root->left, low, high);
+  }
+}