Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.
Example 1:
Input: l1 = [1,2,4], l2 = [1,3,4]
Output: [1,1,2,3,4,4]
Example 2:
Input: l1 = [], l2 = []
Output: []
Example 3:
Input: l1 = [], l2 = [0]
Output: [0]
Constraints:
The number of nodes in both lists is in the range [0, 50].
-100 <= Node.val <= 100
Both l1 and l2 are sorted in non-decreasing order.
Solution:1
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43/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
// if (l1 == null) return l2;
// if (l2 == null) return l1;
// ListNode res;
// if (l1.val < l2.val) {
// res = l1;
// res.next = mergeTwoLists(l1.next, l2);
// } else {
// res = l2;
// res.next = mergeTwoLists(l1, l2.next);
// }
// return res;
ListNode head = new ListNode(0);
ListNode res = head;
while (l1 != null && l2 != null) {
if (l1.val <= l2.val) {
res.next = l1;
l1 = l1.next;
} else {
res.next = l2;
l2 = l2.next;
}
res = res.next;
}
if (l1 != null) {
res.next = l1;
} else if (l2 != null) {
res.next = l2;
}
return head.next;
}
}