leetcode 234. Palindrome Linked List

234. Palindrome Linked List:[题目链接]https://leetcode.com/problems/palindrome-linked-list/)

AC code:

struct ListNode*  reverse(struct ListNode* head){
    struct ListNode* pre = NULL;
    struct ListNode* cur = head;
    struct ListNode* next = NULL;
    while (cur != NULL){
        next = cur->next;
        cur->next = pre;
        pre = cur;
        cur = next;
    }
    return pre;
}

// 1->2->2->1
bool isPalindrome(struct ListNode* head){
    if (head == NULL || head->next == NULL) {
        return true;
    }
    struct ListNode* fast = head, * slow = head;
    // 通过快慢指针找到中间节点
    while (fast->next !=NULL && fast->next->next != NULL) {
        slow = slow->next;
        fast = fast->next->next;
    }
    
    struct ListNode* p = slow->next; // p: 2->1
    slow->next = NULL; // 将head: 1->2 的尾节点置NULL
    p =  reverse(p);   // 逆转p   p: 1->2
    // 分别遍历 head:1->2  p:1->2 
    while (head != NULL && p!= NULL) {
        if (head->val != p->val){
            return false; 
        }
        head = head->next;
        p = p->next;
    }
    
    // // 当链表元素为奇数时 如果有剩余元素
    // if (head != NULL || p != NULL) {
    //     return true;
    // }
    return true;
    
}