validate-binary-search-tree solved

Author: hsskey

validate-binary-search-tree/hsskey.js

@@ -0,0 +1,27 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isValidBST = function(root) {
+    const dfs = (node, left = null, right = null) => {
+        if(!node) {
+            return true
+        }
+
+        if((left !== null && node.val <= left) || (right !== null && node.val >= right)) {
+            return false
+        }
+
+        return dfs(node.left, left, node.val) && dfs(node.right, node.val, right)
+    }
+
+    return dfs(root)
+};