Merge_Two_Sorted_Lists_021.py

'''
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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4
'''


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


class Solution(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if not l1 or not l2:
            return l1 or l2
        head = cur = ListNode(0)
        while l1 and l2:
            if l1.val < l2.val:
                cur.next = l1
                l1 = l1.next
            else:
                cur.next = l2
                l2 = l2.next
            cur = cur.next
        cur.next = l1 or l2
        return head.next


class Solution_Recursive(object):
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if not l1 or not l2:
            return l1 or l2

        if l1.val < l2.val:
            print('l1.val:', l1.val)
            l1.next = self.mergeTwoLists(l1.next, l2)
            return l1
        else:
            print('l2.val:', l2.val)
            l2.next = self.mergeTwoLists(l1, l2.next)
            return l2