148. Sort List

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def sortList(self, head: ListNode) -> ListNode:
        if head == None or head.next == None:
            return head
        temp = head
        slow = head
        fast = head
        while fast != None and fast.next != None:
            temp = slow
            slow = slow.next
            fast = fast.next.next
        temp.next = None
        left_side = self.sortList(head)
        right_side = self.sortList(slow)
        return self.mergeList(left_side, right_side)
    
    def mergeList(self,l1,l2):
        sorted_temp = ListNode(0)
        curr = sorted_temp
        while l1 != None and l2 != None:
            if(l1.val < l2.val):
                curr.next = l1
                l1 = l1.next
            else:
                curr.next = l2
                l2 = l2.next
            curr = curr.next
        
        if l1 != None:
            curr.next = l1
            l1 = l1.next
        if l2 != None:
            curr.next = l2
            l2 = l2.next
        return sorted_temp.next