86. Partition List

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本文详细解析了一种链表分区算法，该算法能够确保所有小于给定值x的节点出现在大于或等于x的节点之前，同时保持各分区内部节点的原始相对顺序。通过实例输入输出展示了算法效果。

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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.

Example:

Input: head = 1->4->3->2->5->2, x = 3
Output: 1->2->2->4->3->5

public ListNode partition(ListNode head, int x) {
        if (head == null) return null;
        List<Integer> lList = new ArrayList<>();
        List<Integer> rList = new ArrayList<>();
        while (true) {
            if (head.val < x) {
                lList.add(head.val);
            } else {
                rList.add(head.val);
            }
            if (head.next == null) {
                break;
            }
            head = head.next;
        }

        lList.addAll(rList);
        ListNode index = new ListNode(0);
        ListNode result = new ListNode(0);
        for (int i = 0; i < lList.size(); i++) {
            index.next = new ListNode(lList.get(i));
            index = index.next;
            if (i == 0) {
                result = index;
            }
        }
        return result;
    }