LeetCode 21. 合并兩個有序連結清單 Merge Two Sorted Lists

将兩個有序連結清單合并為一個新的有序連結清單并傳回。新連結清單是通過拼接給定的兩個連結清單的所有節點組成的。 

示例：

輸入：1->2->4, 1->3->4
輸出：1->1->2->3->4->4
           

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode p1 = l1;
        ListNode p2 = l2;
        
        ListNode fakeHead = new ListNode(0);
        ListNode p = fakeHead;
 
        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 fakeHead.next;
    }
}