添加 98验证二叉搜索树Java简洁代码

problems/0098.验证二叉搜索树.md

@@ -304,6 +304,35 @@ class Solution {
         return true;
     }
 }
+
+// 简洁实现·递归解法
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return validBST(Long.MIN_VALUE, Long.MAX_VALUE, root);
+    }
+    boolean validBST(long lower, long upper, TreeNode root) {
+        if (root == null) return true;
+        if (root.val <= lower || root.val >= upper) return false;
+        return validBST(lower, root.val, root.left) && validBST(root.val, upper, root.right);
+    }
+}
+// 简洁实现·中序遍历
+class Solution {
+    private long prev = Long.MIN_VALUE;
+    public boolean isValidBST(TreeNode root) {
+        if (root == null) {
+            return true;
+        }
+        if (!isValidBST(root.left)) {
+            return false;
+        }
+        if (root.val <= prev) { // 不满足二叉搜索树条件
+            return false;
+        }
+        prev = root.val;
+        return isValidBST(root.right);
+    }
+}
 ```
 
 Python：