feat: add python and java solutions to lcci question

添加《程序员面试金典》题解：面试题 04.05. 合法二叉搜索树

Author: yanglbme

lcci/04.05.Legal Binary Search Tree/README.md

@@ -6,20 +6,72 @@
 
 ## 解法
 <!-- 这里可写通用的实现逻辑 -->
-
+一棵合法的二叉搜索树，其中序遍历的结果应该升序排列。
 
 ### Python3
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    res, t = True, None
+    def isValidBST(self, root: TreeNode) -> bool:
+        self.isValid(root)
+        return self.res
 
+    def isValid(self, root):
+        if not root:
+            return
+        self.isValid(root.left)
+        if self.t is None or self.t < root.val:
+            self.t = root.val
+        else:
+            self.res = False
+            return
+        self.isValid(root.right)
 ```
 
 ### Java
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    private boolean res = true;
+    private Integer t = null;
+    public boolean isValidBST(TreeNode root) {
+        isValid(root);
+        return res;
+    }
 
+    private void isValid(TreeNode root) {
+        if (root == null) {
+            return;
+        }
+        isValid(root.left);
+        if (t == null || t < root.val) {
+            t = root.val;
+        } else {
+            res = false;
+            return;
+        }
+        isValid(root.right);
+    }
+}
 ```
 
 ### ...

lcci/04.05.Legal Binary Search Tree/README_EN.md

@@ -1,49 +1,125 @@
-# [04.05. Legal Binary Search Tree](https://leetcode-cn.com/problems/legal-binary-search-tree-lcci)
-
-## Description
-<p>Implement a function to check if a binary tree is a binary search tree.</p>
-
-<p><strong>Example&nbsp;1:</strong></p>
-
-<pre>
-<strong>Input:</strong>
-    2
-   / \
-  1   3
-<strong>Output:</strong> true
-</pre>
-
-<p><strong>Example&nbsp;2:</strong></p>
-
-<pre>
-<strong>Input:</strong>
-    5
-   / \
-  1   4
-&nbsp;    / \
-&nbsp;   3   6
-<strong>Output:</strong> false
-<strong>Explanation:</strong> Input: [5,1,4,null,null,3,6].
-&nbsp;    the value of root node is 5, but its right child has value 4.</pre>
-
-
-
-## Solutions
-
-
-### Python3
-
-```python
-
-```
-
-### Java
-
-```java
-
-```
-
-### ...
-```
-
-```
+# [04.05. Legal Binary Search Tree](https://leetcode-cn.com/problems/legal-binary-search-tree-lcci)
+
+## Description
+<p>Implement a function to check if a binary tree is a binary search tree.</p>
+
+
+
+<p><strong>Example&nbsp;1:</strong></p>
+
+
+
+<pre>
+
+<strong>Input:</strong>
+
+    2
+
+   / \
+
+  1   3
+
+<strong>Output:</strong> true
+
+</pre>
+
+
+
+<p><strong>Example&nbsp;2:</strong></p>
+
+
+
+<pre>
+
+<strong>Input:</strong>
+
+    5
+
+   / \
+
+  1   4
+
+&nbsp;    / \
+
+&nbsp;   3   6
+
+<strong>Output:</strong> false
+
+<strong>Explanation:</strong> Input: [5,1,4,null,null,3,6].
+
+&nbsp;    the value of root node is 5, but its right child has value 4.</pre>
+
+
+
+
+## Solutions
+
+
+### Python3
+
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    res, t = True, None
+    def isValidBST(self, root: TreeNode) -> bool:
+        self.isValid(root)
+        return self.res
+
+    def isValid(self, root):
+        if not root:
+            return
+        self.isValid(root.left)
+        if self.t is None or self.t < root.val:
+            self.t = root.val
+        else:
+            self.res = False
+            return
+        self.isValid(root.right)
+```
+
+### Java
+
+```java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    private boolean res = true;
+    private Integer t = null;
+    public boolean isValidBST(TreeNode root) {
+        isValid(root);
+        return res;
+    }
+
+    private void isValid(TreeNode root) {
+        if (root == null) {
+            return;
+        }
+        isValid(root.left);
+        if (t == null || t < root.val) {
+            t = root.val;
+        } else {
+            res = false;
+            return;
+        }
+        isValid(root.right);
+    }
+}
+```
+
+### ...
+```
+
+```

lcci/04.05.Legal Binary Search Tree/Solution.java

@@ -0,0 +1,31 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    private boolean res = true;
+    private Integer t = null;
+    public boolean isValidBST(TreeNode root) {
+        isValid(root);
+        return res;
+    }
+
+    private void isValid(TreeNode root) {
+        if (root == null) {
+            return;
+        }
+        isValid(root.left);
+        if (t == null || t < root.val) {
+            t = root.val;
+        } else {
+            res = false;
+            return;
+        }
+        isValid(root.right);
+    }
+}

lcci/04.05.Legal Binary Search Tree/Solution.py

@@ -0,0 +1,23 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    res, t = True, None
+    def isValidBST(self, root: TreeNode) -> bool:
+        self.isValid(root)
+        return self.res
+
+    def isValid(self, root):
+        if not root:
+            return
+        self.isValid(root.left)
+        if self.t is None or self.t < root.val:
+            self.t = root.val
+        else:
+            self.res = False
+            return
+        self.isValid(root.right)