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MergeTwoSortedLists.java
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MergeTwoSortedLists.java
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package com.hncboy;
/**
* @author hncboy
* @date 2019/9/21 19:13
* @description 21.合并两个有序链表
*
* 将两个升序链表合并为一个新的 升序 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。
*
* 示例 1:
* 输入:l1 = [1,2,4], l2 = [1,3,4]
* 输出:[1,1,2,3,4,4]
*
* 示例 2:
* 输入:l1 = [], l2 = []
* 输出:[]
*
* 示例 3:
* 输入:l1 = [], l2 = [0]
* 输出:[0]
*
* 提示:
* 两个链表的节点数目范围是 [0, 50]
* -100 <= Node.val <= 100
* l1 和 l2 均按 非递减顺序 排列
*
* 来源:力扣(LeetCode)
* 链接:https://leetcode-cn.com/problems/merge-two-sorted-lists
* 著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。
*/
public class MergeTwoSortedLists {
public static void main(String[] args) {
ListNode l1 = new ListNode(1);
l1.next = new ListNode(2);
l1.next.next = new ListNode(4);
ListNode l2 = new ListNode(1);
l2.next = new ListNode(3);
l2.next.next = new ListNode(4);
System.out.println(new MergeTwoSortedLists().mergeTwoLists(l1, l2));
}
/**
* 递归
*/
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}
if (l1.val < l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
}
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
/**
* 迭代
*/
public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
ListNode preHead = new ListNode(-1);
ListNode prev = preHead;
while (l1 != null && l2 != null) {
if (l2.val >= l1.val) {
prev.next = l1;
l1 = l1.next;
} else {
prev.next = l2;
l2 = l2.next;
}
prev = prev.next;
}
prev.next = l1 == null ? l2 : l1;
return preHead.next;
}
private static class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
}
}
}