Time: 0 ms (100%), Space: 45.2 MB (49.46%) - LeetHub

Author: JeonJe

0098-validate-binary-search-tree/0098-validate-binary-search-tree.java

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+/**
+ * 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 {
+    public boolean isValidBST(TreeNode root) {
+        return isValid(root, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
+    }
+
+    private boolean isValid(TreeNode node, double min, double max) {
+        if(node == null) {
+            return true;
+        }
+        if(node.val <= min || node.val >= max) {
+            return false;
+        }
+        return isValid(node.left, min, node.val) && isValid(node.right, node.val, max);
+    }
+}