is valid BST

Author: genkimaru

src/main/java/com/leetcode/binarytree/BSTValidator.java

@@ -0,0 +1,42 @@
+package com.leetcode.binarytree;
+
+
+import com.leetcode.util.BinarySearchTree;
+import com.leetcode.util.TreeNode;
+
+
+public class BSTValidator {
+
+    public boolean isValidBST(TreeNode root) {
+        if (root.left != null) {
+            if (root.val < root.left.val) {
+                return false;
+            }
+           return  isValidBST(root.left);
+
+        }
+        if (root.right != null) {
+
+            if (root.val > root.right.val) {
+                return false;
+            }
+          return   isValidBST(root.right);
+        }
+        return true;
+    }
+
+    public static void main(String[] args) {
+        int[] arr = {3, 4, 2, 5, 1, 6};
+
+
+        TreeNode node1 = new TreeNode(3);
+        TreeNode node2 = new TreeNode(4);
+        TreeNode node3 = new TreeNode(5);
+        node1.right = node2;
+        node2.left = node3;
+
+        TreeNode root = BinarySearchTree.buildBST(arr);
+        boolean validBST = new BSTValidator().isValidBST(node1);
+        System.out.println(validBST);
+    }
+}

src/main/java/com/leetcode/util/TreeNode.java

@@ -5,9 +5,9 @@
  */
 
 public class TreeNode {
-    int val;
-    TreeNode left;
-    TreeNode right;
+    public int val;
+    public TreeNode left;
+    public TreeNode right;
 
     public TreeNode() {
     }