算法--链表的分化

import java.util.*;

/*

public class ListNode {

    int val;

    ListNode next = null;

    ListNode(int val) {

        this.val = val;

    }

}*/

public class Divide {

    public ListNode listDivide(ListNode head, int val) {

        ListNode smallHead = null, smallTail = null;

        ListNode bigHead = null, bigTail = null;

        ListNode next = null;

        while (head != null) {

            next = head.next;

            head.next = null;

            if (head.val <= val) {

                if (smallHead == null) {

                    smallHead = head;

                    smallTail = head;

                } else {

                    smallTail.next = head;

                    smallTail = head;

                }

            } else {

                if (bigHead == null) {

                    bigHead = head;

                    bigTail = head;

                } else {

                    bigTail.next = head;

                    bigTail = head;

                }

            }

            head = next;

        }

        // 拼接

        if (smallTail != null)

            smallTail.next = bigHead;

        return smallHead == null ? bigHead : smallHead;

    }

}