Palindrome Linked List
Problem Statement - link #
Given the head of a singly linked list, return true if it is a palindrome.
Examples #
Example 1:
Input: head = [1,2,2,1]
Output: true
Example 2:
Input: head = [1,2]
Output: false
Constraints #
The number of nodes in the list is in the range [1, 10^5].0 <= Node.val <= 9
Solutions #
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* reverse(ListNode* head) {
ListNode* prev = nullptr;
ListNode* curr = head;
while (curr) {
ListNode* next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
return prev;
}
bool isPalindrome(ListNode* head) {
if(!head) return true;
ListNode* slow = head;
ListNode* fast = head;
while(fast && fast->next){
slow = slow->next;
fast = fast->next->next;
}
if(fast) slow = slow->next;
slow = reverse(slow);
while(slow){
if(head->val != slow->val) return false;
head = head->next;
slow = slow->next;
}
return true;
}
};