Create palindrome_linked_list.cpp

C++/palindrome_linked_list.cpp

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+#include<iostream>
+using namespace std;
+
+// Definition for singly-linked list node
+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:
+    bool isPalindrome(ListNode* head) {
+        if (head == nullptr || head->next == nullptr)
+            return true;  // Empty list or single node is palindrome
+
+        // Step 1: Find the middle of the linked list using slow and fast pointers
+        ListNode *slow = head;
+        ListNode *fast = head;
+
+        while (fast->next != nullptr && fast->next->next != nullptr) {
+            slow = slow->next;
+            fast = fast->next->next;
+        }
+
+        // Step 2: Reverse the second half of the linked list
+        ListNode *secondHalf = reverseList(slow->next);
+
+        // Step 3: Compare first half with reversed second half
+        ListNode *firstHalf = head;
+        while (secondHalf != nullptr) {
+            if (firstHalf->val != secondHalf->val)
+                return false;
+            firstHalf = firstHalf->next;
+            secondHalf = secondHalf->next;
+        }
+
+        return true;
+    }
+
+private:
+    // Helper function to reverse a linked list
+    ListNode* reverseList(ListNode* head) {
+        ListNode *prev = nullptr;
+        ListNode *curr = head;
+
+        while (curr != nullptr) {
+            ListNode *next = curr->next;  // Store next node
+            curr->next = prev;            // Reverse the link
+            prev = curr;                  // Move prev one step forward
+            curr = next;                  // Move curr one step forward
+        }
+
+        return prev;  // New head of reversed list
+    }
+};
+
+// Main function to test the solution
+int main() {
+    // Create a sample palindrome linked list: 1->2->2->1
+    ListNode* head = new ListNode(1);
+    head->next = new ListNode(2);
+    head->next->next = new ListNode(2);
+    head->next->next->next = new ListNode(1);
+
+    Solution solution;
+    bool isPalindrome = solution.isPalindrome(head);
+
+    // Print result
+    if (isPalindrome)
+        cout << "The linked list is a palindrome" << endl;
+    else
+        cout << "The linked list is not a palindrome" << endl;
+
+    // Clean up memory (delete the linked list)
+    while (head != nullptr) {
+        ListNode* temp = head;
+        head = head->next;
+        delete temp;
+    }
+
+    return 0;
+}