CODE 47. Partition List

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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.

public ListNode partition(ListNode head, int x) {
	// Start typing your Java solution below
	// DO NOT write main() function
	ListNode p1 = new ListNode(0);
	ListNode q1 = new ListNode(0);
	ListNode p2 = p1;
	ListNode q2 = q1;

	while (head != null) {
		if (x > head.val) {
			p2.next = new ListNode(head.val);
			p2 = p2.next;
		} else {
			q2.next = new ListNode(head.val);
			q2 = q2.next;
		}
		head = head.next;
	}
	if (null != q1.next) {
		p2.next = q1.next;
	}
	return p1.next;
}