21. Merge Two Sorted Lists

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.

/** * 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 presult = new ListNode(0);       ListNode p = presult;              while(p1 != null && p2 != null){           if(p1.val >= p2.val){               p.next = p2;               p2 = p2.next;           }else{               p.next = p1;               p1 = p1.next;           }           p = p.next;       }       if(p1 != null){           p.next = p1;       }       if(p2 != null){           p.next = p2;       }              return presult.next;      }    }