题解 | #合并两个排序的链表#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode Merge(ListNode list1, ListNode list2) {
        if (list1 == null) {
            return list2;
        }
        if (list2 == null) {
            return list1;
        }

        ListNode l1 = list1;
        ListNode l2 = list2;
        ListNode res = new ListNode(-1);
        ListNode p = res;

        //p l1 l2三个节点永远是三角关系，p在l1和l2之间选择较小的值连接
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                p.next = l1;
                l1 = l1.next;
            } else {
                p.next = l2;
                l2 = l2.next;
            }

            p = p.next;
        }

        //有一个链表到头了，p接上另一个链表
        if (l1 == null) {
            p.next = l2;
        }
        if (l2 == null) {
            p.next = l1;
        }

        return res.next;
    }
}