Add solution #865

Author: JoshCrozier

README.md

@@ -672,6 +672,7 @@
 862|[Shortest Subarray with Sum at Least K](./0862-shortest-subarray-with-sum-at-least-k.js)|Hard|
 863|[All Nodes Distance K in Binary Tree](./0863-all-nodes-distance-k-in-binary-tree.js)|Medium|
 864|[Shortest Path to Get All Keys](./0864-shortest-path-to-get-all-keys.js)|Hard|
+865|[Smallest Subtree with all the Deepest Nodes](./0865-smallest-subtree-with-all-the-deepest-nodes.js)|Medium|
 867|[Transpose Matrix](./0867-transpose-matrix.js)|Easy|
 868|[Binary Gap](./0868-binary-gap.js)|Easy|
 872|[Leaf-Similar Trees](./0872-leaf-similar-trees.js)|Easy|

solutions/0865-smallest-subtree-with-all-the-deepest-nodes.js

@@ -0,0 +1,44 @@
+/**
+ * 865. Smallest Subtree with all the Deepest Nodes
+ * https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/
+ * Difficulty: Medium
+ *
+ * Given the root of a binary tree, the depth of each node is the shortest distance to the root.
+ *
+ * Return the smallest subtree such that it contains all the deepest nodes in the original tree.
+ *
+ * A node is called the deepest if it has the largest depth possible among any node in the entire
+ * tree.
+ *
+ * The subtree of a node is a tree consisting of that node, plus the set of all descendants of
+ * that node.
+ */
+
+/**
+ * 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 {TreeNode}
+ */
+var subtreeWithAllDeepest = function(root) {
+  return findDepthAndNode(root).node;
+
+  function findDepthAndNode(node) {
+    if (!node) return { depth: 0, node: null };
+
+    const left = findDepthAndNode(node.left);
+    const right = findDepthAndNode(node.right);
+
+    if (left.depth === right.depth) {
+      return { depth: left.depth + 1, node: node };
+    }
+    const deeper = left.depth > right.depth ? left : right;
+    return { depth: deeper.depth + 1, node: deeper.node };
+  }
+};