c++代码：判断链表是否为回文链表

#include <iostream>
#include <stack>
using namespace std;

struct ListNode {
    int val;
    ListNode* next;
    ListNode(int x) : val(x), next(NULL) {}
};

bool isPalindrome(ListNode* head) {
    if (!head || !head->next) return true;
    ListNode* slow = head;
    ListNode* fast = head;
    while (fast->next && fast->next->next) {
        slow = slow->next;
        fast = fast->next->next;
    }
    stack<int> s;
    while (slow->next) {
        slow = slow->next;
        s.push(slow->val);
    }
    while (!s.empty()) {
        if (head->val != s.top()) return false;
        s.pop();
        head = head->next;
    }
    return true;
}

int main() {
    ListNode* head = new ListNode(1);
    head->next = new ListNode(2);
    head->next->next = new ListNode(2);
    head->next->next->next = new ListNode(1);
    cout << isPalindrome(head) << endl; // 输出1，即为true
    return 0;
}