Add solution #501

Author: JoshCrozier

0501-find-mode-in-binary-search-tree.js

@@ -0,0 +1,36 @@
+/**
+ * 501. Find Mode in Binary Search Tree
+ * https://leetcode.com/problems/find-mode-in-binary-search-tree/
+ * Difficulty: Easy
+ *
+ * Given the root of a binary search tree (BST) with duplicates, return all
+ * the mode(s) (i.e., the most frequently occurred element) in it.
+ *
+ * If the tree has more than one mode, return them in any order.
+ */
+
+/**
+ * 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 findMode = function(root) {
+  const map = new Map();
+  dfs(root);
+
+  function dfs(root) {
+    if (!root) return 0;
+    map.set(root.val, (map.get(root.val) || 0) + 1);
+    [root.left, root.right].forEach(dfs);
+  }
+
+  const max = Math.max(...map.values());
+  return Array.from(map.keys()).filter(key => map.get(key) === max);
+};

README.md

@@ -163,6 +163,7 @@
 491|[Non-decreasing Subsequences](./0491-non-decreasing-subsequences.js)|Medium|
 492|[Construct the Rectangle](./0492-construct-the-rectangle.js)|Easy|
 500|[Keyboard Row](./0500-keyboard-row.js)|Easy|
+501|[Find Mode in Binary Search Tree](./0501-find-mode-in-binary-search-tree.js)|Easy|
 506|[Relative Ranks](./0506-relative-ranks.js)|Easy|
 509|[Fibonacci Number](./0509-fibonacci-number.js)|Easy|
 520|[Detect Capital](./0520-detect-capital.js)|Easy|