题解 | #类似将链表以某个值分开#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode sortCowsIV (ListNode head) {
        // write code here
        // 1. 处理特殊情况
        if (head == null || head.next == null) return head;

        // 2. 遍历处理
        ListNode bs = null, as = null;
        ListNode be = null, ae = null;
        while (head != null) {
            if (head.val == 0) {
                if (bs == null) {
                    bs = head;
                    be = head;
                } else {
                    be.next = head;
                    be = be.next;
                }
            } else {
                if (as == null) {
                    as = head;
                    ae = head;
                } else {
                    ae.next = head;
                    ae = ae.next;
                }
            }
            head = head.next;
        }

        // 3. 处理特殊情况
        if (bs == null) return as;
        be.next = as;
        if (ae != null)
            ae.next = null;

        return bs;
    }
}