LeetCode 21. 合并两个有序链表(Merge Two Sorted Lists)

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

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;

        }

    }

}

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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

LeetCode 21. 合并两个有序链表(Merge Two Sorted Lists)的相关教程结束。