剑指offer第36题 合并两个排序的链表

输入两个递增排序的链表，合并这两个链表并使新链表中的结点仍然是按照递增排序的。

算法1

(递归)

Java 代码

class Solution {
    public ListNode merge(ListNode l1, ListNode l2) {
        if(l1 == null) return l2;
        if(l2 == null) return l1;

        ListNode p = null;
        if(l1.val <= l2.val){
            l1.next = merge(l1.next, l2);
            return l1;
        }else{
            l2.next = merge(l1, l2.next);
            return l2;
        }
    }
}

算法2

(迭代)

Java 代码

class Solution {
    public ListNode merge(ListNode l1, ListNode l2) {
        if(l1 == null && l2 == null) return null;
        ListNode res = new ListNode(0), cur = res;

        while(l1 != null && l2 != null){
            if(l1.val < l2.val){
                cur.next = l1;
                l1 = l1.next;
            }else{
                cur.next = l2;
                l2 = l2.next;
            }
            cur = cur.next;
        }

        cur.next = (l1 == null? l2: l1);

        return res.next;
    }
}