Add solution #968

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,052 LeetCode solutions in JavaScript
+# 1,053 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -776,6 +776,7 @@
 965|[Univalued Binary Tree](./solutions/0965-univalued-binary-tree.js)|Easy|
 966|[Vowel Spellchecker](./solutions/0966-vowel-spellchecker.js)|Medium|
 967|[Numbers With Same Consecutive Differences](./solutions/0967-numbers-with-same-consecutive-differences.js)|Medium|
+968|[Binary Tree Cameras](./solutions/0968-binary-tree-cameras.js)|Hard|
 970|[Powerful Integers](./solutions/0970-powerful-integers.js)|Easy|
 976|[Largest Perimeter Triangle](./solutions/0976-largest-perimeter-triangle.js)|Easy|
 977|[Squares of a Sorted Array](./solutions/0977-squares-of-a-sorted-array.js)|Easy|

solutions/0968-binary-tree-cameras.js

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+/**
+ * 968. Binary Tree Cameras
+ * https://leetcode.com/problems/binary-tree-cameras/
+ * Difficulty: Hard
+ *
+ * You are given the root of a binary tree. We install cameras on the tree nodes where each camera
+ * at a node can monitor its parent, itself, and its immediate children.
+ *
+ * Return the minimum number of cameras needed to monitor all nodes of the tree.
+ */
+
+/**
+ * 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 {number}
+ */
+var minCameraCover = function(root) {
+  let cameras = 0;
+  const rootState = traverse(root);
+  return rootState === 0 ? cameras + 1 : cameras;
+
+  function traverse(node) {
+    if (!node) return 1;
+
+    const left = traverse(node.left);
+    const right = traverse(node.right);
+
+    if (left === 0 || right === 0) {
+      cameras++;
+      return 2;
+    }
+
+    if (left === 2 || right === 2) {
+      return 1;
+    }
+
+    return 0;
+  }
+};