LeetCode进阶之路（Merge Two Sorted Lists）

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Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

题目：两个有序的链表组合成一个有序的新链表。

思路：因为是有序的，所以把每个节点都取出来放到一个list里重新排序，再放到新链表里即可。

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        if(l1 == null) {            return l2;        }        if(l2 == null) {            return l1;        }        ListNode newNode = new ListNode(0);        ListNode head = newNode;        List<Integer> list = new ArrayList<Integer>();        while(l1 != null) {            list.add(l1.val);            l1 = l1.next;        }        while(l2 != null) {            list.add(l2.val);            l2 = l2.next;        }        Collections.sort(list);        for(Integer integer : list){            ListNode n = new ListNode(integer);            head.next = n;            head = head.next;        }        return newNode.next;    }

7.26更新

这个方法也用指针来解决，时间复杂度会减少很多。

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        ListNode node = new ListNode(-1);        ListNode head = node;        ListNode first = l1;        ListNode second = l2;        while(first != null || second != null){            if(first != null && second !=null){                if(first.val < second.val) {                    head.next = first;                    first = first.next;                    head = head.next;                }else {                    head.next = second;                    second = second.next;                    head = head.next;                }                            }else if(first == null) {                head.next = second;                break;            } else {                head.next = first;                break;            }        }        return node.next;                }

种一棵树最好的时间是十年前，其次是现在！

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