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LeetCode 234

请判断一个链表是否为回文链表。

  • 示例 1:

    1
    2
    输入: 1->2
    输出: false

  • 示例 2:

    1
    2
    输入: 1->2->2->1
    输出: true

解决参照之前练习题：查找中间节点 和 反转列表 应用结合起来：

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class Solution {
public:    
    ListNode* reverseList(ListNode* head) {
        if(head==NULL||head->next==NULL)
            return head;
        ListNode *p=reverseList(head->next);
        head->next->next=head;
        head->next=NULL;
        return p;

    }
    
    ListNode* middleNode(ListNode* head) {
        if (head == NULL)
            return head;
        
        ListNode *slow = head;
        ListNode *fast = head;
        
        while (fast && fast->next){
            slow = slow->next;
            fast = fast->next->next;
        }
        
        return slow;
    }
    
    bool isPalindrome(ListNode* head) {
        ListNode *mid =  middleNode(head);
        ListNode *slow = reverseList(mid);
        
        while(head&&slow)
        {
            if(head->val!=slow->val)
                return false;
            else
            {
                head=head->next;
                slow=slow->next;
            }
        }
        return true;
    }
};