Leetcode

# 23. Merge k Sorted Lists

by hooni posted Apr 14, 2020
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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```

```/**
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode mergeKLists(ListNode[] lists) {
/*
ListNode result = lists[0];
ListNode last = result;

for(int i=1; i<lists.length; i++){
while(last.next != null){
last = last.next;
}
ListNode tmp = lists[i];
last.next = tmp;
}
return result;
*/
if(lists.length == 0){
return null;
}

ListNode left = null;
int index = 0;
while(index<lists.length && left==null){
if(lists[index] != null){
left = lists[index];
}
index++;
}

while(index<lists.length){
if(lists[index] != null){
ListNode right = lists[index];
left = merge(left, right);
}
index++;
}

return left;
}

public ListNode merge(ListNode left, ListNode right){
if(left == null){
return right;
}

if(right == null){
return left;
}

ListNode result = null;
if(left.val < right.val){
result = left;
result.next = merge(left.next, right);
}else{
result = right;
result.next = merge(left, right.next);
}

return result;
}
}```

[문제] https://leetcode.com/problems/merge-k-sorted-lists/

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