题解 | 链表的奇偶重排

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 oddEvenList (ListNode head) {
        // write code here
        if(head == null) return null;
        List<ListNode> oddList = new ArrayList<>();
        ListNode oddNode = head;
        while (true) {
            if (oddNode == null) break;
            oddList.add(oddNode);
            if (oddNode.next == null || oddNode.next.next == null) break;
            oddNode = oddNode.next.next;
        }

        List<ListNode> evenList = new ArrayList<>();
        ListNode evenNode = head.next;
        while (true) {
            if (evenNode == null) break;
            evenList.add(evenNode);
            if (evenNode.next == null) break;
            evenNode = evenNode.next.next;
        }

        ListNode targetNode = oddList.get(0);
        for(int i=1;i<oddList.size();i++){
            targetNode.next = oddList.get(i);
            targetNode = targetNode.next;
            targetNode.next = null;
        }

        for(int i=0;i<evenList.size();i++){
            targetNode.next = evenList.get(i);
            targetNode = targetNode.next;
            targetNode.next = null;
        }

        return head;
    }
}