leetcode hot 03

解题思路：找个容器将这个链表遍历一遍存下来，然后再对比；或者用数组列表存下来，双指针前后对比

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        if(head == null){
            return false;
        }
        ListNode dummy_head = new ListNode();
        ListNode p = head;
        while(p!=null){
            ListNode q = new ListNode(p.val,dummy_head.next);
            dummy_head.next = q;
            p = p.next;
        }
        ListNode head1 = dummy_head.next;
        while(head1!=null){
            if(head1.val!=head.val) return false;
            head1 = head1.next;
            head = head.next;
        }
        return true;

    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        //  数组加双指针
        List<Integer> list = new ArrayList<>();
        while(head!=null){
            list.add(head.val);
            head = head.next;
        }
        int left = 0;
        int right = list.size()-1;
        while(left<right){
            if(list.get(left) != list.get(right)) return false;
            left++;
            right--;
        }
        return true;
    }
}