Add solution #1261

Author: JoshCrozier

README.md

@@ -456,6 +456,7 @@
 1233|[Remove Sub-Folders from the Filesystem](./1233-remove-sub-folders-from-the-filesystem.js)|Medium|
 1249|[Minimum Remove to Make Valid Parentheses](./1249-minimum-remove-to-make-valid-parentheses.js)|Medium|
 1252|[Cells with Odd Values in a Matrix](./1252-cells-with-odd-values-in-a-matrix.js)|Easy|
+1261|[Find Elements in a Contaminated Binary Tree](./1261-find-elements-in-a-contaminated-binary-tree.js)|Medium|
 1267|[Count Servers that Communicate](./1267-count-servers-that-communicate.js)|Medium|
 1268|[Search Suggestions System](./1268-search-suggestions-system.js)|Medium|
 1287|[Element Appearing More Than 25% In Sorted Array](./1287-element-appearing-more-than-25-in-sorted-array.js)|Easy|

solutions/1261-find-elements-in-a-contaminated-binary-tree.js

@@ -0,0 +1,57 @@
+/**
+ * 1261. Find Elements in a Contaminated Binary Tree
+ * https://leetcode.com/problems/find-elements-in-a-contaminated-binary-tree/
+ * Difficulty: Medium
+ *
+ * Given a binary tree with the following rules:
+ * 1. root.val == 0
+ * 2. For any treeNode:
+ *   1. If treeNode.val has a value x and treeNode.left != null,
+ *      then treeNode.left.val == 2 * x + 1
+ *   2. If treeNode.val has a value x and treeNode.right != null,
+ *      then treeNode.right.val == 2 * x + 2
+ *
+ * Now the binary tree is contaminated, which means all treeNode.val have
+ * been changed to -1.
+ *
+ * Implement the FindElements class:
+ * - FindElements(TreeNode* root) Initializes the object with a contaminated binary
+ *   tree and recovers it.
+ * - bool find(int target) Returns true if the target value exists in the recovered
+ *   binary 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
+ */
+var FindElements = function(root) {
+  this.values = new Set();
+  root.val = 0;
+
+  const traverse = node => {
+    if (!node) return;
+    this.values.add(node.val);
+    if (node.left) node.left.val = 2 * node.val + 1;
+    if (node.right) node.right.val = 2 * node.val + 2;
+    traverse(node.left);
+    traverse(node.right);
+  };
+
+  traverse(root);
+};
+
+/**
+ * @param {number} target
+ * @return {boolean}
+ */
+FindElements.prototype.find = function(target) {
+  return this.values.has(target);
+};