Add solution #23

Author: JoshCrozier

README.md

@@ -25,6 +25,7 @@
 20|[Valid Parentheses](./0020-valid-parentheses.js)|Easy|
 21|[Merge Two Sorted Lists](./0021-merge-two-sorted-lists.js)|Easy|
 22|[Generate Parentheses](./0022-generate-parentheses.js)|Medium|
+23|[Merge k Sorted Lists](./0023-merge-k-sorted-lists.js)|Hard|
 24|[Swap Nodes in Pairs](./0024-swap-nodes-in-pairs.js)|Medium|
 27|[Remove Element](./0027-remove-element.js)|Easy|
 28|[Implement strStr()](./0028-implement-strstr.js)|Easy|

solutions/0023-merge-k-sorted-lists.js

@@ -0,0 +1,43 @@
+/**
+ * 23. Merge k Sorted Lists
+ * https://leetcode.com/problems/merge-k-sorted-lists/
+ * Difficulty: Hard
+ *
+ * You are given an array of k linked-lists lists, each linked-list is sorted
+ * in ascending order.
+ *
+ * Merge all the linked-lists into one sorted linked-list and return it.
+ */
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode[]} lists
+ * @return {ListNode}
+ */
+var mergeKLists = function(lists) {
+  const map = new Map();
+  for (let list of lists) {
+    while (list) {
+      map.set(list.val, (map.get(list.val) || 0) + 1);
+      list = list.next;
+    }
+  }
+  const sorted = [...map].sort(([a], [b]) => a - b);
+  const result = new ListNode();
+  let tail = result;
+
+  for (let [key, value] of sorted) {
+    while (value--) {
+      tail.next = new ListNode(key);
+      tail = tail.next;
+    }
+  }
+
+  return result.next;
+};