添加题450，110

Author: ligecarryme

算法思维/二叉搜索树.md

@@ -43,3 +43,73 @@ function insertIntoBST(root: TreeNode | null, val: number): TreeNode | null {
 };
 ```
 
+##### [450. 删除二叉搜索树中的节点](https://leetcode-cn.com/problems/delete-node-in-a-bst/)
+
+给定一个二叉搜索树的根节点 root 和一个值 key，删除二叉搜索树中的 key 对应的节点，并保证二叉搜索树的性质不变。返回二叉搜索树（有可能被更新）的根节点的引用。
+
+> 思路：[秒懂就完事了](https://leetcode-cn.com/problems/delete-node-in-a-bst/solution/miao-dong-jiu-wan-shi-liao-by-terry2020-tc0o/)
+
+```tsx
+
+function deleteNode(root: TreeNode | null, key: number): TreeNode | null {
+    if (root === null) {
+        return root
+    }
+    if (root.val < key) {
+        root.right = deleteNode(root.right, key)
+    } else if (root.val > key) {
+        root.left = deleteNode(root.left, key)
+    } else {
+        if (root.left === null) {
+            return root.right
+        } else if (root.right === null) {
+            return root.left
+        } else {
+            let cur: TreeNode = root.right
+            while (cur.left !== null) {
+                cur = cur.left
+            }
+            cur.left = root.left
+            return root.right
+        }
+    }
+    return root
+};
+```
+
+##### [110. 平衡二叉树](https://leetcode-cn.com/problems/balanced-binary-tree/)
+
+给定一个二叉树，判断它是否是高度平衡的二叉树。
+
+```js
+const isBalanced = function (root) {
+    if (maxDepth(root) === -1) {
+        return false
+    }
+    return true
+};
+
+const maxDepth = function (root) {
+    if (root === null) {
+        return 0
+    }
+    const left = maxDepth(root.left)
+    const right = maxDepth(root.right)
+    if (left === -1 || right === -1 || Math.abs(right - left) > 1) {
+        return -1
+    }
+    if (left > right) {
+        return left + 1
+    } else {
+        return right + 1
+    }
+}
+```
+
+## 练习
+
+-  [validate-binary-search-tree](https://leetcode-cn.com/problems/validate-binary-search-tree/)
+-  [insert-into-a-binary-search-tree](https://leetcode-cn.com/problems/insert-into-a-binary-search-tree/)
+-  [delete-node-in-a-bst](https://leetcode-cn.com/problems/delete-node-in-a-bst/)
+-  [balanced-binary-tree](https://leetcode-cn.com/problems/balanced-binary-tree/)
+