分割链表

/*
 * Problem: Partition a linked list such that all nodes less than x come before nodes greater than or equal to x.
 * Approach (Java Streams simulation):
 * 1. Since Java Streams are not directly applicable to linked lists in this way, 
 *    simulate the functionality by creating helper methods.
 * 2. This example simulates stream processing without using Java Streams.
 */

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public ListNode partition(ListNode head, int x) {
        List<ListNode> nodes = new ArrayList<>();
        ListNode current = head;
        // Collect nodes into a list
        while (current != null) {
            nodes.add(current);
            current = current.next;
        }
        // Partition nodes by the value x
        List<ListNode> lessThanX = new ArrayList<>();
        List<ListNode> greaterOrEqualX = new ArrayList<>();
        for (ListNode node : nodes) {
            if (node.val < x) {
                lessThanX.add(node);
            } else {
                greaterOrEqualX.add(node);
            }
        }
        // Combine lists
        ListNode dummy = new ListNode(0);
        current = dummy;
        for (ListNode node : lessThanX) {
            current.next = node;
            current = current.next;
        }
        for (ListNode node : greaterOrEqualX) {
            current.next = node;
            current = current.next;
        }
        current.next = null; // End the list
        return dummy.next;
    }
}