剑指 Offer 25. 合并两个排序的链表

/**
 * 剑指 Offer 25. 合并两个排序的链表
 * @author wsq
 * @date 2020/09/09
	 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节点仍然是递增排序的。
	
	示例1：
	输入：1->2->4, 1->3->4
	输出：1->1->2->3->4->4
	
	限制：
	0 <= 链表长度 <= 1000
	
	链接：https://leetcode-cn.com/problems/he-bing-liang-ge-pai-xu-de-lian-biao-lcof
 */
package notsubmit;

public class MergeTwoLists {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    	ListNode head = null;
    	if(l1 == null) {
    		return l2;
    	}
    	if(l2 == null) {
    		return l1;
    	}
    	if(l1.val <= l2.val) {
    		head = l1;
    		l1 = l1.next;
    	}else {
    		head = l2;
    		l2 = l2.next;
    	}
    	
    	ListNode p = head;
    	
    	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;
    	}
    	if(l1 != null) {
    		p.next = l1;
    	}
    	if(l2 != null) {
    		p.next = l2;
    	}
    	return head;
    }
}