669. 修剪二叉搜索树

Author: w2xi

README.md

@@ -143,6 +143,7 @@
 |645|[错误的集合](https://leetcode.cn/problems/set-mismatch/)|[JavaScript](./algorithms/set-mismatch.js)|Easy|
 |654|[最大二叉树](https://leetcode.cn/problems/maximum-binary-tree/)|[JavaScript](./algorithms/maximum-binary-tree.js)|Medium|
 |657|[机器人能否返回原点](https://leetcode.cn/problems/robot-return-to-origin/)|[JavaScript](./algorithms/robot-return-to-origin.js)|Easy|
+|669|[修剪二叉搜索树](https://leetcode.cn/problems/trim-a-binary-search-tree/)|[JavaScript](./algorithms/trim-a-binary-search-tree.js)|Medium|
 |682|[棒球比赛](https://leetcode.cn/problems/baseball-game/)|[JavaScript](./algorithms/baseball-game.js)|Easy|
 |687|[最长同值路径](https://leetcode.cn/problems/longest-univalue-path/)|[JavaScript](./algorithms/longest-univalue-path.js)|Medium|
 |700|[二叉搜索树中的搜索](https://leetcode.cn/problems/search-in-a-binary-search-tree/)|[JavaScript](./algorithms/search-in-a-binary-search-tree.js)|Easy|

algorithms/trim-a-binary-search-tree.js

@@ -0,0 +1,35 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} low
+ * @param {number} high
+ * @return {TreeNode}
+ */
+var trimBST = function (root, low, high) {
+  // 后序遍历
+  if (!root) return null;
+  root.left = trimBST(root.left, low, high);
+  root.right = trimBST(root.right, low, high);
+  if (root.val < low || root.val > high) {
+    // 叶节点
+    if (!root.left && !root.right) {
+      return null;
+    }
+    // 左节点不存在
+    if (!root.left) {
+      return root.right;
+    }
+    // 右节点不存在
+    if (!root.right) {
+      return root.left;
+    }
+  }
+  return root;
+};