Binary Search Tree Iterator

Author: charlesbuczel

0173_binarySearchTreeIterator.js

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+/**
+ * @typedef {Object} TreeNode
+ * @description Definition for a binary tree node.
+ * @example
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+
+/**
+ * Iterator over a binary search tree
+ * @summary Binary Search Tree Iterator {@link https://leetcode.com/problems/binary-search-tree-iterator/}
+ * @description Given a root node of BST, implement an iterator that returns smallest available number.
+ */
+class BSTIterator {
+  constructor(root) {
+    this.node = root;
+    this.stack = [];
+  }
+
+  /**
+   * Space O(1) , Time O(1)
+   */
+  hasNext() {
+    return this.node || this.stack.length;
+  }
+
+  /**
+   * Space O(n) - worst case stack will have all nodes.
+   * Time O(n) - worst case iterate over all nodes.
+   */
+  next() {
+    while (this.node) {
+      this.stack.push(this.node);
+      this.node = this.node.left;
+    }
+
+    this.node = this.stack.pop();
+    const result = this.node.val;
+    this.node = this.node.right;
+
+    return result;
+  }
+}