Palindrome Linked List - Amazon Top Interview Questions


Problem Statement :


Given a singly linked list node whose values are integers, determine whether the linked list forms a palindrome.

Constraints

n ≤ 100,000 where n is the length of node

Example 1

Input

node = [5, 3, 5]

Output

True

Explanation

5 -> 3 -> 5 is a palindrome.

Example 2

Input

node = [12, 8, 12]

Output

True

Explanation

The values of the linked list are the same forwards and backwards.



Solution :



title-img




                        Solution in C++ :

bool checkPalindrome(LLNode *node, LLNode **curr) {
    if (node == NULL) return true;
    bool check = checkPalindrome(node->next, curr);
    if (node->val != (*curr)->val) return false;
    *curr = (*curr)->next;
    return check;
}
bool solve(LLNode *node) {
    LLNode *curr = node;
    return checkPalindrome(node, &curr);
}
                    




                        Solution in Python : 
                            
class Solution:
    def solve(self, node):
        fast, slow = node, node
        while fast and fast.next:
            fast = fast.next.next
            slow = slow.next

        right = None
        while slow:
            p = slow.next
            slow.next = right
            right = slow
            slow = p

        left = node
        while left is not None and right is not None:
            if left.val != right.val:
                return False
            left = left.next
            right = right.next
        return True
                    


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