feat: update leetcode solutions: No.0098. Validate Binary Search Tree

Author: yanglbme

solution/0000-0099/0098.Validate Binary Search Tree/README.md

@@ -41,22 +41,67 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
+中序遍历，若是一个有效的二叉搜索树，那么遍历到的序列应该是单调递增的。所以只要比较判断遍历到的当前数是否 `>=` 上一个数即可。
+
 <!-- tabs:start -->
 
 ### **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, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    pre = None
+    def isValidBST(self, root: TreeNode) -> bool:
+        if not root:
+            return True
+        if not self.isValidBST(root.left):
+            return False
+        if self.pre is not None and self.pre >= root.val:
+            return False
+        self.pre = root.val
+        if not self.isValidBST(root.right):
+            return False
+        return True
 ```
 
 ### **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() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    private Integer pre = null;
+    public boolean isValidBST(TreeNode root) {
+        if (root == null) return true;
+        if (!isValidBST(root.left)) return false;
+        if (pre != null && pre >= root.val) return false;
+        pre = root.val;
+        if (!isValidBST(root.right)) return false;
+        return true;
+    }
+}
 ```
 
 ### **...**

solution/0000-0099/0098.Validate Binary Search Tree/README_EN.md

@@ -65,13 +65,56 @@
 ### **Python3**
 
 ```python
-
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    pre = None
+    def isValidBST(self, root: TreeNode) -> bool:
+        if not root:
+            return True
+        if not self.isValidBST(root.left):
+            return False
+        if self.pre is not None and self.pre >= root.val:
+            return False
+        self.pre = root.val
+        if not self.isValidBST(root.right):
+            return False
+        return True
 ```
 
 ### **Java**
 
 ```java
-
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    private Integer pre = null;
+    public boolean isValidBST(TreeNode root) {
+        if (root == null) return true;
+        if (!isValidBST(root.left)) return false;
+        if (pre != null && pre >= root.val) return false;
+        pre = root.val;
+        if (!isValidBST(root.right)) return false;
+        return true;
+    }
+}
 ```
 
 ### **...**

solution/0000-0099/0098.Validate Binary Search Tree/Solution.java

@@ -1,13 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
 class Solution {
-
-    private long current = Long.MIN_VALUE;
-
+    private Integer pre = null;
     public boolean isValidBST(TreeNode root) {
         if (root == null) return true;
-        if (isValidBST(root.left) && current < root.val) {
-            current = root.val;
-            return isValidBST(root.right);
-        }
-        return false;
+        if (!isValidBST(root.left)) return false;
+        if (pre != null && pre >= root.val) return false;
+        pre = root.val;
+        if (!isValidBST(root.right)) return false;
+        return true;
     }
 }

solution/0000-0099/0098.Validate Binary Search Tree/Solution.py

@@ -0,0 +1,19 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    pre = None
+    def isValidBST(self, root: TreeNode) -> bool:
+        if not root:
+            return True
+        if not self.isValidBST(root.left):
+            return False
+        if self.pre is not None and self.pre >= root.val:
+            return False
+        self.pre = root.val
+        if not self.isValidBST(root.right):
+            return False
+        return True