[Solved] Given the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions.

Question

Given the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

Example 1:

Input: head = [1,4,3,2,5,2], x = 3
Output: [1,2,2,4,3,5]

Example 2:

Input: head = [2,1], x = 2
Output: [1,2]

Constraints:

• The number of nodes in the list is in the range [0, 200].
• -100 <= Node.val <= 100
• -200 <= x <= 200

Python Solution

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def partition(self, head: ListNode, x: int) -> ListNode:    
        l1 = ListNode(0)
        y = l1
        l2 = ListNode(0)
        z = l2
        head1 = head
        while head1:
            if head1.val < x:
                l1.next = ListNode(head1.val)
                l1 = l1.next
            else:
                l2.next = ListNode(head1.val)
                l2 = l2.next
            head1 = head1.next
        l1.next = z.next
        return y.next