Merge Two Sorted Lists

问题描述

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.

算法

代码一

public ListNode mergeTwoLists(ListNode l1,ListNode l2){
        if(l1==null)
            return l2;
        if(l2==null)
            return l1;
        ListNode l3,p;
        if(l1.val<=l2.val){
            l3=l1;
            p=l1;
            l1=l1.next;
        }else{
            l3=l2;
            p=l2;
            l2=l2.next;
        }
        while(l1!=null&&l2!=null){
            if(l1.val<=l2.val){
                p.next=l1;
                l1=l1.next;
                p=p.next;
            }else{
                p.next=l2;
                l2=l2.next;
                p=p.next;
            }
        }
        if(l1==null){
            p.next=l2;
        }else{
            p.next=l1;
        }
        return l3;
    }

代码二

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    if (l1 == null || l2 == null) {
        return l1 == null ? l2 : l1;
    }
    ListNode head = null;
    if (l1.val < l2.val) {
        head = l1;
        head.next = mergeTwoLists(l1.next, l2);
    } else {
        head = l2;
        head.next = mergeTwoLists(l1, l2.next);
    }
    return head;
}