LeetCode86 Partition List

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本文详细解析了一种链表分区算法，该算法能够将链表中所有小于给定值x的节点放置在大于等于x的节点之前，同时保持各部分内部的原始相对顺序不变。通过实例演示了输入为1->4->3->2->5->2，x=3时，输出为1->2->2->4->3->5的过程。文章提供了完整的Java实现代码，包括创建链表、打印链表和执行分区操作的方法。

题目：

Given a linked list and a value x, partition it such that all nodes less than xcome 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 static ListNode partition(ListNode head, int x) {
        if (head == null || head.next == null)
            return head;

        ListNode dummySmall = new ListNode(0);
        ListNode dummyBig = new ListNode(0);
        ListNode cur1 = dummySmall;
        ListNode cur2 = dummyBig;

        while (head != null) {
            if (head.val < x) {
                cur1.next = head;
                cur1 = cur1.next;
            } else {
                cur2.next = head;
                cur2 = cur2.next;
            }
            head = head.next;
        }
        cur1.next = dummyBig.next;
        cur2.next = null;
        return dummySmall.next;

    }

    public static ListNode createLinkedList(int arr[], int n){
        if (n == 0)
            return null;
        ListNode head = new ListNode(arr[0]);
        ListNode cur = head;
        for (int i = 1; i < n; i++) {
            cur.next = new ListNode(arr[i]);
            cur = cur.next;
        }

        return head;
    }

    public static void printLinkedList(ListNode head){
        ListNode cur = head;
        while (cur != null){
            System.out.print(cur.val + " -> ");
            cur = cur.next;
        }
        System.out.println("NULL");
    }

    public static void main(String[] args) {
        int[] arr = {1, 4, 3, 2, 5, 2};
        ListNode head = createLinkedList(arr, arr.length);
        printLinkedList(head);

        ListNode node = partition(head, 3);
        printLinkedList(node);
        
    }
}