Validate Binary Search Tree

Author: iam-edwin

validate-binary-search-tree/iam-edwin.java

@@ -0,0 +1,52 @@
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return (root.left == null || isValidBSTMax(root.left, root.val))
+                && (root.right == null || isValidBSTMin(root.right, root.val));
+    }
+
+    private boolean isValidBSTMax(TreeNode root, int max) {
+        if (root.val >= max) {
+            return false;
+        }
+
+        return (root.left == null || isValidBSTMax(root.left, root.val))
+                && (root.right == null || isValidBSTMinMax(root.right, root.val, max));
+    }
+
+    private boolean isValidBSTMin(TreeNode root, int min) {
+        if (root.val <= min) {
+            return false;
+        }
+
+        return (root.left == null || isValidBSTMinMax(root.left, min, root.val))
+                && (root.right == null || isValidBSTMin(root.right, root.val));
+    }
+
+    private boolean isValidBSTMinMax(TreeNode root, int min, int max) {
+        if (root.val >= max || root.val <= min) {
+            return false;
+        }
+
+        return (root.left == null || isValidBSTMinMax(root.left, min, root.val))
+                && (root.right == null || isValidBSTMinMax(root.right, root.val, max));
+    }
+
+    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;
+        }
+    }
+}