MergeKSortedLists.py

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

class Solution:
    def mergeTwoLists(self, l1, l2):
        if l1 is None:
            return l2
        if l2 is None:
            return l1
        if l1.val<l2.val:
            l1.next=self.mergeTwoLists(l1.next,l2)
            return l1
        else:
            l2.next=self.mergeTwoLists(l1,l2.next)
            return l2
    # @param a list of ListNode
    # @return a ListNode
    def mergeKLists(self, lists):
        if len(lists)==0:
            return None
        if len(lists)==1:
            return lists[0]
        head = lists[0]
        for x in xrange(1,len(lists)):
            head=self.mergeTwoLists(head,lists[x])
        return head