{"id":6889,"date":"2025-06-17T19:29:12","date_gmt":"2025-06-17T13:59:12","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=6889"},"modified":"2025-06-17T19:44:51","modified_gmt":"2025-06-17T14:14:51","slug":"palindrome-linked-list","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/palindrome-linked-list\/","title":{"rendered":"Palindrome Linked List"},"content":{"rendered":"\n<!-- PrismJS for Syntax Highlighting -->\n<link href=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/themes\/prism-tomorrow.min.css\" rel=\"stylesheet\">\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/prism.min.js\"><\/script>\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/plugins\/autoloader\/prism-autoloader.min.js\"><\/script>\n\n<style>\n    .wp_blog_main-heading {\n      text-align: center;\n      font-size: 2.4rem;\n      color: #E58C32;\n      margin-top: 2.5rem;\n      font-weight: bold;\n    }\n    \n    .wp_blog_explanation,\n    .wp_blog_code-tabs-container {\n      max-width: 940px;\n      margin: 2rem auto;\n      padding: 2rem;\n      border-radius: 12px;\n      background-color: #f9fafb;\n    }\n    \n    .wp_blog_explanation h2 {\n      font-size: 1.4rem;\n      color: #E58C32;\n      margin-bottom: 0.75rem;\n    }\n    \n    .wp_blog_explanation p,\n    .wp_blog_explanation li {\n      font-size: 1.05rem;\n      line-height: 1.7;\n      margin: 0.5rem 0;\n      color: #1f2937;\n    }\n    \n    .wp_blog_explanation code {\n      padding: 3px 6px;\n      border-radius: 4px;\n      background: #e5e7eb;\n      font-family: 'Courier New', monospace;\n    }\n    \n    .wp_blog_code-tabs-header {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 0.5rem;\n      margin-bottom: 1rem;\n    }\n    \n    .wp_blog_code-tab-button {\n      padding: 0.6rem 1.2rem;\n      border: 1px solid #E58C32;\n      color: #E58C32;\n      border-radius: 50px;\n      font-weight: 600;\n      cursor: pointer;\n      background-color: white;\n      transition: background 0.3s ease, color 0.3s ease;\n    }\n    \n    .wp_blog_code-tab-button.active {\n      background: #E58C32;\n      color: white;\n    }\n    \n    .wp_blog_code-tab-content {\n      display: none;\n      background: #111827;\n      border-radius: 12px;\n    }\n    \n    .wp_blog_code-tab-content.active {\n      display: block;\n    }\n    \n    .wp_blog_code-tab-content pre {\n      margin: 0;\n      padding: 1.5rem;\n      font-size: 1rem;\n      overflow-x: auto;\n      color: #f3f4f6;\n      background: #111827;\n      border-radius: 12px;\n    }\n    <\/style>\n<div class=\"wp_blog_explanation\">\n  <h2>Problem Statement:<\/h2>\n  <p>\n    Given the <code>head<\/code> of a singly linked list, return <code>true<\/code> if it is a palindrome or <code>false<\/code> otherwise.\n  <\/p>\n\n  <h2>Examples:<\/h2>\n  <ul>\n    <li><strong>Input:<\/strong> head = [1,2,2,1]<br><strong>Output:<\/strong> true<\/li>\n    <li><strong>Input:<\/strong> head = [1,2]<br><strong>Output:<\/strong> false<\/li>\n  <\/ul>\n\n  <h2>Constraints:<\/h2>\n  <ul>\n    <li>The number of nodes in the list is in the range [1, 10<sup>5<\/sup>].<\/li>\n    <li>0 <= Node.val <= 9<\/li>\n  <\/ul>\n\n  <h2>Approach 1:<\/h2>\n  <ul>\n    <li>Traverse the linked list and store values in an array.<\/li>\n    <li>Check whether the array is a palindrome by comparing elements from start and end moving towards the center.<\/li>\n  <\/ul>\n\n  <h2>Time and Space Complexity:<\/h2>\n  <ul>\n    <li><strong>Time Complexity:<\/strong> O(n), where n is the number of nodes.<\/li>\n    <li><strong>Space Complexity:<\/strong> O(n), for the array storage.<\/li>\n  <\/ul>\n<\/div>\n\n<div class=\"wp_blog_code-tabs-container\">\n  <div class=\"wp_blog_code-tabs-header\">\n    <button class=\"wp_blog_code-tab-button active\" data-lang=\"js\">JavaScript<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"py\">Python<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"java\">Java<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"cpp\">C++<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"c\">C<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"cs\">C#<\/button>\n  <\/div>\n\n  <!-- JavaScript -->\n  <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n    <pre><code class=\"language-javascript\">\nvar isPalindrome = function(head) {\n    let arr = [];\n    let curr = head;\n    while (curr !== null) {\n        arr.push(curr.val);\n        curr = curr.next;\n    }\n    let left = 0, right = arr.length - 1;\n    while (left < right) {\n        if (arr[left++] !== arr[right--]) return false;\n    }\n    return true;\n};\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- Python -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n    <pre><code class=\"language-python\">\nclass Solution(object):\n    def isPalindrome(self, head):\n        vals = []\n        while head:\n            vals.append(head.val)\n            head = head.next\n        return vals == vals[::-1]\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- Java -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n    <pre><code class=\"language-java\">\nclass Solution {\n    public boolean isPalindrome(ListNode head) {\n        List<Integer> vals = new ArrayList<>();\n        while (head != null) {\n            vals.add(head.val);\n            head = head.next;\n        }\n        int left = 0, right = vals.size() - 1;\n        while (left < right) {\n            if (!vals.get(left++).equals(vals.get(right--))) return false;\n        }\n        return true;\n    }\n}\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C++ -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"cpp\">\n    <pre><code class=\"language-cpp\">\nclass Solution {\npublic:\n    bool isPalindrome(ListNode* head) {\n        vector&ltint&gt vals;\n        while (head) {\n            vals.push_back(head->val);\n            head = head->next;\n        }\n        int left = 0, right = vals.size() - 1;\n        while (left < right) {\n            if (vals[left++] != vals[right--]) return false;\n        }\n        return true;\n    }\n};\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"c\">\n    <pre><code class=\"language-c\">\nbool isPalindrome(struct ListNode* head) {\n    int vals[100000], i = 0, left, right;\n    while (head) {\n        vals[i++] = head->val;\n        head = head->next;\n    }\n    left = 0; right = i - 1;\n    while (left < right) {\n        if (vals[left++] != vals[right--]) return false;\n    }\n    return true;\n}\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C# -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n    <pre><code class=\"language-csharp\">\npublic class Solution {\n    public bool IsPalindrome(ListNode head) {\n        List&ltint&gt vals = new List&ltint&gt();\n        while (head != null) {\n            vals.Add(head.val);\n            head = head.next;\n        }\n        int left = 0, right = vals.Count - 1;\n        while (left < right) {\n            if (vals[left++] != vals[right--]) return false;\n        }\n        return true;\n    }\n}\n    <\/code><\/pre>\n  <\/div>\n<\/div>\n<div class=\"wp_blog_explanation\">\n  <h2>Approach 2:<\/h2>\n  <ul>\n    <li>Use two pointers (<code>slow<\/code> and <code>fast<\/code>) to find the middle of the linked list.<\/li>\n    <li>Reverse the second half of the list.<\/li>\n    <li>Compare the first and second halves node by node.<\/li>\n  <\/ul>\n\n  <h2>Time and Space Complexity:<\/h2>\n  <ul>\n    <li><strong>Time Complexity:<\/strong> O(n)<\/li>\n    <li><strong>Space Complexity:<\/strong> O(1)<\/li>\n  <\/ul>\n<\/div>\n\n<div class=\"wp_blog_code-tabs-container\">\n  <div class=\"wp_blog_code-tabs-header\">\n    <button class=\"wp_blog_code-tab-button active\" data-lang=\"js\">JavaScript<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"py\">Python<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"java\">Java<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"cpp\">C++<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"c\">C<\/button>\n    <button class=\"wp_blog_code-tab-button\" data-lang=\"cs\">C#<\/button>\n  <\/div>\n\n  <!-- JavaScript -->\n  <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n    <pre><code class=\"language-javascript\">\nvar isPalindrome = function(head) {\n    let slow = head, fast = head;\n\n    while (fast && fast.next) {\n        slow = slow.next;\n        fast = fast.next.next;\n    }\n\n    \/\/ Reverse second half\n    let prev = null;\n    while (slow) {\n        let temp = slow.next;\n        slow.next = prev;\n        prev = slow;\n        slow = temp;\n    }\n\n    \/\/ Compare two halves\n    let first = head, second = prev;\n    while (second) {\n        if (first.val !== second.val) return false;\n        first = first.next;\n        second = second.next;\n    }\n\n    return true;\n};\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- Python -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n    <pre><code class=\"language-python\">\nclass Solution:\n    def isPalindrome(self, head):\n        slow = fast = head\n        while fast and fast.next:\n            slow = slow.next\n            fast = fast.next.next\n\n        # Reverse second half\n        prev = None\n        while slow:\n            temp = slow.next\n            slow.next = prev\n            prev = slow\n            slow = temp\n\n        # Compare halves\n        first, second = head, prev\n        while second:\n            if first.val != second.val:\n                return False\n            first = first.next\n            second = second.next\n\n        return True\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- Java -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n    <pre><code class=\"language-java\">\nclass Solution {\n    public boolean isPalindrome(ListNode head) {\n        ListNode slow = head, fast = head;\n\n        while (fast != null && fast.next != null) {\n            slow = slow.next;\n            fast = fast.next.next;\n        }\n\n        \/\/ Reverse second half\n        ListNode prev = null;\n        while (slow != null) {\n            ListNode temp = slow.next;\n            slow.next = prev;\n            prev = slow;\n            slow = temp;\n        }\n\n        \/\/ Compare halves\n        ListNode first = head, second = prev;\n        while (second != null) {\n            if (first.val != second.val) return false;\n            first = first.next;\n            second = second.next;\n        }\n\n        return true;\n    }\n}\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C++ -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"cpp\">\n    <pre><code class=\"language-cpp\">\nclass Solution {\npublic:\n    bool isPalindrome(ListNode* head) {\n        ListNode *slow = head, *fast = head;\n\n        while (fast && fast->next) {\n            slow = slow->next;\n            fast = fast->next->next;\n        }\n\n        \/\/ Reverse second half\n        ListNode* prev = nullptr;\n        while (slow) {\n            ListNode* temp = slow->next;\n            slow->next = prev;\n            prev = slow;\n            slow = temp;\n        }\n\n        \/\/ Compare halves\n        ListNode* first = head;\n        while (prev) {\n            if (first->val != prev->val) return false;\n            first = first->next;\n            prev = prev->next;\n        }\n\n        return true;\n    }\n};\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"c\">\n    <pre><code class=\"language-c\">\nbool isPalindrome(struct ListNode* head) {\n    struct ListNode *slow = head, *fast = head;\n\n    while (fast && fast->next) {\n        slow = slow->next;\n        fast = fast->next->next;\n    }\n\n    \/\/ Reverse second half\n    struct ListNode* prev = NULL;\n    while (slow) {\n        struct ListNode* temp = slow->next;\n        slow->next = prev;\n        prev = slow;\n        slow = temp;\n    }\n\n    \/\/ Compare halves\n    struct ListNode* first = head;\n    while (prev) {\n        if (first->val != prev->val) return false;\n        first = first->next;\n        prev = prev->next;\n    }\n\n    return true;\n}\n    <\/code><\/pre>\n  <\/div>\n\n  <!-- C# -->\n  <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n    <pre><code class=\"language-csharp\">\npublic class Solution {\n    public bool IsPalindrome(ListNode head) {\n        ListNode slow = head, fast = head;\n\n        while (fast != null && fast.next != null) {\n            slow = slow.next;\n            fast = fast.next.next;\n        }\n\n        \/\/ Reverse second half\n        ListNode prev = null;\n        while (slow != null) {\n            ListNode temp = slow.next;\n            slow.next = prev;\n            prev = slow;\n            slow = temp;\n        }\n\n        \/\/ Compare halves\n        ListNode first = head, second = prev;\n        while (second != null) {\n            if (first.val != second.val) return false;\n            first = first.next;\n            second = second.next;\n        }\n\n        return true;\n    }\n}\n    <\/code><\/pre>\n  <\/div>\n<\/div>\n<script>\ndocument.addEventListener('DOMContentLoaded', () => {\n  document.querySelectorAll('.wp_blog_code-tabs-container').forEach(container => {\n    const buttons = container.querySelectorAll('.wp_blog_code-tab-button');\n    const contents = container.querySelectorAll('.wp_blog_code-tab-content');\n\n    buttons.forEach(button => {\n      button.addEventListener('click', () => {\n        const lang = button.getAttribute('data-lang');\n\n        \/\/ Remove 'active' from all buttons and contents in this container only\n        buttons.forEach(btn => btn.classList.remove('active'));\n        contents.forEach(content => content.classList.remove('active'));\n\n        \/\/ Activate the selected button and corresponding content\n        button.classList.add('active');\n        container.querySelector(`.wp_blog_code-tab-content[data-lang=\"${lang}\"]`).classList.add('active');\n      });\n    });\n  });\n});\n<\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>Problem Statement: Given the head of a singly linked list, return true if it is a palindrome or false otherwise. Examples: Input: head = [1,2,2,1]Output: true Input: head = [1,2]Output: false Constraints: The number of nodes in the list is in the range [1, 105]. 0 next; } int left = 0, right = vals.size()<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[260,176,811,810,174,172,173],"tags":[],"class_list":{"0":"post-6889","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-c-c-plus-plus","7":"category-csharp","8":"category-data-structures-and-algorithms","9":"category-dsa","10":"category-java","11":"category-javascript","12":"category-python"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/6889","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/comments?post=6889"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/6889\/revisions"}],"predecessor-version":[{"id":6896,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/6889\/revisions\/6896"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=6889"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=6889"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=6889"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}