21. 合并两个有序链表
21. Merge Two Sorted Lists
题目描述
将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
LeetCode21. Merge Two Sorted Lists
示例:
输入: 1->2->4, 1->3->4
输出: 1->1->2->3->4->4
输出: 1->1->2->3->4->4
Java 实现
ListNode 类
class ListNode {
int val;
ListNode next = null;
ListNode(int val) {
this.val = val;
}
@Override
public String toString() {
return val + "->" + next;
}
}
Iterative Solution
public class Solution {
public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
if (list1 == null && list2 == null) {
return null;
}
if (list1 == null) {
return list2;
}
if (list2 == null) {
return list1;
}
ListNode head = new ListNode(-1);
ListNode curr = head;
while (list1 != null && list2 != null) {
if (list1.val <= list2.val) {
curr.next = list1;
list1 = list1.next;
} else {
curr.next = list2;
list2 = list2.next;
}
curr = curr.next;
}
if (list1 != null) {
curr.next = list1;
}
if (list2 != null) {
curr.next = list2;
}
return head.next;
}
}
Recursive Solution
public class Solution {
public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
if (list1 == null) {
return list2;
}
if (list2 == null) {
return list1;
}
if (list1.val <= list2.val) {
list1.next = mergeTwoLists(list1.next, list2);
return list1;
} else {
list2.next = mergeTwoLists(list1, list2.next);
return list2;
}
}
}
相似题目
参考资料
- https://leetcode.com/problems/merge-two-sorted-lists/
- https://leetcode-cn.com/problems/merge-two-sorted-lists/
- https://leetcode.com/problems/merge-two-sorted-lists/discuss/9715/Java-1-ms-4-lines-codes-using-recursion
- https://leetcode.com/problems/merge-two-sorted-lists/discuss/9858/Java-solution-for-reference