链表---合并n个有序链表

public ListNode mergeKLists(List<ListNode> lists) {
        // write your code here
        if (lists == null || lists.size() == 0) {
            return null;
        }
        ListNode dummy = new ListNode(0);
        ListNode p = dummy;
        Queue<ListNode> queue = new PriorityQueue<ListNode>(lists.size(), new Comparator<ListNode>()
        {   
            @Override
            public int compare(ListNode o1, ListNode o2) {
                return o1.val - o2.val;
            }
        });
        for (ListNode node : lists) {
            if (node != null) {
                queue.offer(node);
            }
        }
        while (!queue.isEmpty()) {
             ListNode node = queue.poll();
                 p.next = node;
                 if (node.next != null) {
                     queue.offer(node.next);
                 }
                 p = p.next;
        }
        return dummy.next;
    }

合并两个有序链表

样例
给出 1->3->8->11->15->null，2->null， 返回 1->2->3->8->11->15->null。

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        // write your code here
        ListNode dummy = new ListNode(-1);
        ListNode p =dummy;
        ListNode p1 = l1;
        ListNode p2 = l2;
        while (p1 != null && p2 != null) {
            if (p1.val < p2.val) {
                p.next = p1;
                p1 = p1.next;
            } else {
                p.next = p2;
                p2 = p2.next;
            }
            p = p.next;
        }
        if (p1 != null) {
            p.next = p1;
        }
        if (p2 != null) {
            p.next = p2;
        }
        return dummy.next;
    }