21_Merge_Two_Sorted_Lists.py

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

class Solution(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if(l1 is None):
            return l2
        elif(l2 is None):
            return l1
        else:
            merged=ListNode(0)
            merged.next=None
            p=merged
            while l1 is not None and l2 is not None:
                if l1.val<l2.val:
                    p.next=l1
                    l1=l1.next
                else:
                    p.next=l2
                    l2=l2.next
                p=p.next
                if l1 is not None:
                    p.next=l1
                else:
                    p.next=l2
            return merged.next