added merge k sorted lists

Author: ignacio-chiazzo

LeetcodeProblems/merge_k_sorted_lists.js

@@ -0,0 +1,95 @@
+/*
+Merge k Sorted Lists
+https://leetcode.com/problems/merge-k-sorted-lists/
+
+Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
+
+Example:
+
+Input:
+[
+  1->4->5,
+  1->3->4,
+  2->6
+]
+Output: 1->1->2->3->4->4->5->6
+*/
+
+var ListNode = require('../utilsClasses/ListNode').ListNode;
+
+var mergeKLists = function(lists) {
+  if(lists.length === 0)
+    return null;
+  
+  var queue = [];
+  for(var i = 0; i < lists.length; i++) 
+    queue.push(lists[i]);
+  
+  while(queue.length > 1) {
+    list1 = queue.shift();
+    list2 = queue.shift();
+    queue.push(mergeLists(list1, list2));
+  }
+  
+  return queue.shift();
+};
+
+var mergeLists = function(list1, list2) {
+  if(list1 === null) {
+    return list2;
+  } else if(list2 === null) 
+    return list1;
+    
+  var iter1 = list1;
+  var iter2 = list2;  
+  var head;
+  
+  if(iter1.val < iter2.val) {
+    head = iter1;
+    iter1 = iter1.next
+  } else {
+    head = iter2;
+    iter2 = iter2.next;
+  }
+
+  var iterHead = head;
+  while(iter1 !== null && iter2 !== null) {
+    if(iter1.val < iter2.val) {
+      iterHead.next = iter1;
+      iter1 = iter1.next;
+    } else {
+      iterHead.next = iter2;
+      iter2 = iter2.next;
+    }
+    iterHead = iterHead.next;
+    iterHead.next = null;
+  }
+  
+  if(iter1 !== null) {
+    iterHead.next = iter1;
+  } else if(iter2 !== null) {
+    iterHead.next = iter2;
+  }
+  
+  return head;
+}
+
+var main = function() {
+  console.log(mergeKLists([]));
+  console.log(mergeKLists(
+    [null]
+  ));
+  console.log(mergeKLists(
+    [null, null]
+  ));
+
+  var list1 = ListNode.linkenList([1,2,3]);
+  var list2 = ListNode.linkenList([2,3,4]);
+  var list3 = ListNode.linkenList([5,6]);
+  var list4 = ListNode.linkenList([1,5]);
+  console.log(mergeKLists(
+    [list1, list2, list3, list4]
+  ));
+}
+
+module.exports.main = main;