Partition List

ID: 86; medium

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Solution 1 (Java)

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode partition(ListNode head, int x) {
        ListNode dummySmall = new ListNode(0);
        ListNode dummyLarge = new ListNode(0);
        ListNode headSmall = dummySmall;
        ListNode headLarge = dummyLarge;
        while (head != null) {
            if (head.val < x) {
                headSmall.next = head;
                headSmall = head;
            } else {
                headLarge.next = head;
                headLarge = head;
            }
            head = head.next;
        }
        headSmall.next = dummyLarge.next;
        headLarge.next = null;
        return dummySmall.next;
    }
}