86. 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.

class Solution {
    public ListNode partition(ListNode head, int x) {
        if(head==null||head.next==null) return head;
        ListNode big = new ListNode(0);
        ListNode small = new ListNode(0);
        ListNode smallhead = small;
        ListNode bighead = big;
        while(head!=null){
            if(head.val<x){ 
                small.next = head;
                small = head;
            }
            else{
                big.next = head;
                big = head;
            }
            head = head.next;
        }
        big.next = null;
        small.next = bighead.next;
        return smallhead.next;
    }
   
}