解析

//!  n,n
class Solution {
 public:
  bool isPalindrome(ListNode *head) {
    stack<int> s;
    ListNode *node = head;
    int len = 0;
    while (node != nullptr) {
      ++len;
      node = node->next;
    }
    node = head;
    for (int i = 0; i < len / 2; ++i) {
      s.emplace(node->val);
      node = node->next;
    }
    if (len % 2 != 0) {
      node = node->next;
    }
    while (node != nullptr && !s.empty()) {
      if (node->val != s.top()) {
        return false;
      }
      node = node->next;
      s.pop();
    }
    return true;
  }
};