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.

合并两个有序链表

/**
 * 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;
    }
}

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param two ListNodes
    # @return a ListNode
    def mergeTwoLists(self, l1, l2):
        if l1 == None:
            return l2
        if l2 == None:
            return l1
        dummy = ListNode(0)
        tmp = dummy
        while l1 and l2:
            if l1.val <= l2.val:
                tmp.next = l1
                l1 = l1.next
                tmp = tmp.next
            else:
                tmp.next = l2
                l2 = l2.next
                tmp = tmp.next
        if l2 == None:
            tmp.next = l1
        else:
            tmp.next = l2
        return dummy.next