Leet Code 23 Merge k Sorted Lists - 合并K个有序链表 Java

[code=language-java]/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public static ListNode mergeKLists(ListNode[] lists) {
if (lists == null || lists.length == 0) {
return null;
}
if (lists.length == 1) {
return lists[0];
} else if (lists.length == 2) {
return mergeTwoLists(lists[0], lists[1]);
} else {
int half = (lists.length & 1) == 0 ? lists.length / 2
: lists.length / 2 + 1;
ListNode[] merged = new ListNode[half];
for (int i = 0; i < half; i++) {
if (lists.length - 1 - i != i) {
merged[i] = mergeTwoLists(lists[i], lists[lists.length - 1 - i]);
} else {
merged[i] = lists[i];
}
}
return mergeKLists(merged);
}
}

public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode dummyHead = new ListNode(0);
ListNode p = dummyHead;
while (l1 != null && l2 != null) {
if (l1.val <= l2.val) {
p.next = l1;
l1 = l1.next;
} else {
p.next = l2;
l2 = l2.next;
}
p = p.next;
}
p.next = l1 != null ? l1 : l2;
return dummyHead.next;
}
}