Add week 7 solutions : validateBinarySearchTree

Author: yolophg

validate-binary-search-tree/yolophg.js

@@ -0,0 +1,34 @@
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+
+var isValidBST = function (root) {
+  if (root === null) {
+    return true;
+  }
+
+  // initialize a queue for BFS.
+  let queue = [];
+  queue.push({ node: root, min: -Infinity, max: Infinity });
+
+  while (queue.length > 0) {
+    // dequeue the front one.
+    let { node, min, max } = queue.shift();
+
+    // check the BST for the current node.
+    if (node.val <= min || node.val >= max) {
+      return false;
+    }
+
+    // enqueue the left child with updated min and max.
+    if (node.left !== null) {
+      queue.push({ node: node.left, min: min, max: node.val });
+    }
+
+    // enqueue the right child with updated min and max.
+    if (node.right !== null) {
+      queue.push({ node: node.right, min: node.val, max: max });
+    }
+  }
+
+  return true;
+};