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Merge k Sorted Lists.js
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Merge k Sorted Lists.js
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/**
Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
*/
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode[]} lists
* @return {ListNode}
*/
var mergeKLists = function(lists) {
var len = lists.length;
if (len === 0) {
return null;
}
if (len === 1) {
return lists[0];
}
return mergeHelper(lists, 0, len - 1);
};
function mergeHelper(lists, start, end) {
if (start === end) {
return lists[start];
}
if (start > end) {
return null;
}
var mid = parseInt((start + end) / 2),
left,
right;
left = mergeHelper(lists, start, mid);
right = mergeHelper(lists, mid + 1, end);
return mergeTwoLists(left, right);
}
function mergeTwoLists(left, right) {
if (!left) {
return right;
}
if (!right) {
return left;
}
var dummy = new ListNode(0),
prev = dummy,
node1 = left,
node2 = right;
while (node1 && node2) {
if (node1.val < node2.val) {
prev.next = node1;
node1 = node1.next;
} else {
prev.next = node2;
node2 = node2.next;
}
prev = prev.next;
}
if (node1) {
prev.next = node1;
}
if (node2) {
prev.next = node2;
}
return dummy.next;
}