Parition List

Given 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.

For example, Given 1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5.

Solution

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

class Solution(object):
    def partition(self, head, x):
        """
        :type head: ListNode
        :type x: int
        :rtype: ListNode
        """
        head1, head2 = ListNode(0), ListNode(0)
        p1, p2 = head1, head2
        p = head
        while p:
            if p.val < x:
                p1.next = p
                p = p.next
                p1 = p1.next
                p1.next = None
            else:
                p2.next = p
                p = p.next
                p2 = p2.next
                p2.next = None
        p1.next = head2.next
        head = head1.next
        return head