Add solution #958

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,043 LeetCode solutions in JavaScript
+# 1,044 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -767,6 +767,7 @@
 955|[Delete Columns to Make Sorted II](./solutions/0955-delete-columns-to-make-sorted-ii.js)|Medium|
 956|[Tallest Billboard](./solutions/0956-tallest-billboard.js)|Hard|
 957|[Prison Cells After N Days](./solutions/0957-prison-cells-after-n-days.js)|Medium|
+958|[Check Completeness of a Binary Tree](./solutions/0958-check-completeness-of-a-binary-tree.js)|Medium|
 966|[Vowel Spellchecker](./solutions/0966-vowel-spellchecker.js)|Medium|
 970|[Powerful Integers](./solutions/0970-powerful-integers.js)|Easy|
 976|[Largest Perimeter Triangle](./solutions/0976-largest-perimeter-triangle.js)|Easy|

solutions/0958-check-completeness-of-a-binary-tree.js

@@ -0,0 +1,41 @@
+/**
+ * 958. Check Completeness of a Binary Tree
+ * https://leetcode.com/problems/check-completeness-of-a-binary-tree/
+ * Difficulty: Medium
+ *
+ * Given the root of a binary tree, determine if it is a complete binary tree.
+ *
+ * In a complete binary tree, every level, except possibly the last, is completely filled, and
+ * all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes
+ * inclusive at the last level h.
+ */
+
+/**
+ * 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 isCompleteTree = function(root) {
+  const queue = [root];
+  let foundNull = false;
+
+  while (queue.length) {
+    const node = queue.shift();
+    if (!node) {
+      foundNull = true;
+      continue;
+    }
+    if (foundNull) return false;
+    queue.push(node.left);
+    queue.push(node.right);
+  }
+
+  return true;
+};