2-7.cpp

#include <iostream>
#include <stack>
using namespace std;
class Node
{
public:
    int value;
    Node *next;
    Node(int v) : value(v) {}
};
/*
1 2 3 2 3

1 2 3 2

*/
bool check_pal(Node *head)
{
    stack<int> temp;
    Node *fast = head;
    Node *slow = head;
    while (!(fast == NULL || fast->next == NULL)) { //important logic
        temp.push(slow->value);
        slow = slow->next;
        fast = fast->next->next;
    }
    if (fast != NULL) {
        slow = slow->next;
    }
    while (!temp.empty()) {
        if (temp.top() != slow->value) {
            return false;
        }
        temp.pop();
        slow = slow->next;
    }
    return true;
}

int main(int argc, char *argv[]) {
    Node *head = new Node(1);
    Node *a = new Node(2);
    Node *b = new Node(3);
    Node *c = new Node(2);
    Node *d = new Node(3);
    head->next = a;
    a->next = b;
    b->next = c;
    c->next = d;
    
    cout << check_pal(head) << endl;
    
    return 0;
}