{"id":2310,"date":"2026-07-20T12:41:36","date_gmt":"2026-07-20T10:41:36","guid":{"rendered":"https:\/\/kindsonthegenius.com\/blog\/everything-about-linked-list-with-python-code-and-hackerrank-leetcode-solutions\/"},"modified":"2026-08-27T17:40:29","modified_gmt":"2026-08-27T15:40:29","slug":"everything-about-linked-list-with-python-code-and-hackerrank-leetcode-solutions","status":"publish","type":"post","link":"https:\/\/kindsonthegenius.com\/blog\/everything-about-linked-list-with-python-code-and-hackerrank-leetcode-solutions\/","title":{"rendered":"Everything About Linked List With Python Code and HackerRank\/LeetCode Solutions"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><em>Learn linked lists in Python with practical code examples, core operations, two-pointer techniques, and common HackerRank and LeetCode problem-solving patterns.<\/em><\/p>\n\n\n<p><!-- ktg-updated-banner --><\/p>\n<p><em>Updated August 2026 \u2014 full tutorial restored for this URL.<\/em><\/p>\n<h2>TL;DR<\/h2>\n<ul>\n<li>\n<p>Linked lists store data in connected nodes, making insertion and deletion efficient when you already have the target node.<\/p>\n<\/li>\n<li>\n<p>Learn the core operations: insert, delete, traverse, and reverse a singly linked list in Python.<\/p>\n<\/li>\n<li>\n<p>Dummy nodes simplify linked list operations by reducing edge cases, especially when modifying the head.<\/p>\n<\/li>\n<li>\n<p>Two-pointer techniques solve common problems such as finding the middle node and detecting cycles.<\/p>\n<\/li>\n<li>\n<p>Practice patterns like merging sorted lists, reversing lists, removing nodes, and detecting cycles for HackerRank and LeetCode.<\/p>\n<\/li>\n<\/ul>\n<p>This is a practical <strong>linked list<\/strong> guide in <strong>Python<\/strong>: structure, core operations, and patterns that show up on HackerRank \/ LeetCode. Also see <a href=\"https:\/\/kindsonthegenius.com\/blog\/how-to-reverse-a-linked-list\/\">How to Reverse a Linked List<\/a>.<\/p>\n<ol>\n<li><a href=\"#t1\">Singly linked list basics<\/a><\/li>\n<li><a href=\"#t2\">Insert and delete<\/a><\/li>\n<li><a href=\"#t3\">Traverse and reverse<\/a><\/li>\n<li><a href=\"#t4\">Two-pointer patterns (middle, cycle)<\/a><\/li>\n<li><a href=\"#t5\">Merge two sorted lists<\/a><\/li>\n<li><a href=\"#t6\">Practice checklist<\/a><\/li>\n<\/ol>\n<p><strong id=\"t1\">1. Singly linked list basics<\/strong><\/p>\n<pre><code>class Node:\n    def __init__(self, val, next=None):\n        self.val = val\n        self.next = next\n\nclass LinkedList:\n    def __init__(self):\n        self.head = None\n<\/code><\/pre>\n<p>Arrays give O(1) index access; linked lists give O(1) insert\/delete at a known node (after you find it).<\/p>\n<p><strong id=\"t2\">2. Insert and delete<\/strong><\/p>\n<pre><code>def push_front(self, val):\n    self.head = Node(val, self.head)\n\ndef delete_val(self, val):\n    dummy = Node(0, self.head)\n    cur = dummy\n    while cur.next:\n        if cur.next.val == val:\n            cur.next = cur.next.next\n            break\n        cur = cur.next\n    self.head = dummy.next\n<\/code><\/pre>\n<p>Dummy nodes simplify edge cases at the head.<\/p>\n<p><strong id=\"t3\">3. Traverse and reverse<\/strong><\/p>\n<pre><code>def to_list(head):\n    out = []\n    while head:\n        out.append(head.val)\n        head = head.next\n    return out\n\ndef reverse(head):\n    prev = None\n    while head:\n        nxt = head.next\n        head.next = prev\n        prev, head = head, nxt\n    return prev\n<\/code><\/pre>\n<p><strong id=\"t4\">4. Two-pointer patterns (middle, cycle)<\/strong><\/p>\n<pre><code>def middle(head):\n    slow = fast = head\n    while fast and fast.next:\n        slow = slow.next\n        fast = fast.next.next\n    return slow\n\ndef has_cycle(head):\n    slow = fast = head\n    while fast and fast.next:\n        slow = slow.next\n        fast = fast.next.next\n        if slow is fast:\n            return True\n    return False\n<\/code><\/pre>\n<p>Floyd\u2019s cycle detection is a classic interview question (LeetCode 141).<\/p>\n<p><strong id=\"t5\">5. Merge two sorted lists<\/strong><\/p>\n<pre><code>def merge(l1, l2):\n    dummy = Node(0)\n    cur = dummy\n    while l1 and l2:\n        if l1.val &lt;= l2.val:\n            cur.next, l1 = l1, l1.next\n        else:\n            cur.next, l2 = l2, l2.next\n        cur = cur.next\n    cur.next = l1 or l2\n    return dummy.next\n<\/code><\/pre>\n<p><strong id=\"t6\">6. Practice checklist<\/strong><\/p>\n<ul>\n<li>Reverse list \/ reverse in k-groups<\/li>\n<li>Remove nth from end (two pointers)<\/li>\n<li>Detect\/start of cycle<\/li>\n<li>Merge k sorted lists (heap)<\/li>\n<li>Copy list with random pointer<\/li>\n<\/ul>\n<p>Draw pointers on paper before coding \u2014 most bugs are lost references, not syntax.<\/p>\n<h2>Final Thought<\/h2>\n<p>Linked lists become much easier once you stop thinking of them as a collection of values and start thinking in terms of <strong>pointers and node references<\/strong>. The most important skill is understanding how changing one <code>next<\/code> reference affects the rest of the list.<\/p>\n<p>The patterns covered here, from dummy nodes and in-place reversal to slow and fast pointers, appear repeatedly in coding interviews and algorithm problems. Before writing code, draw the nodes and trace where each pointer should move. That simple habit can prevent many of the most common linked list bugs.<\/p>\n<p>Once these fundamentals are comfortable, move on to more challenging variations such as reversing nodes in groups, removing the nth node from the end, and merging multiple sorted lists.<\/p>","protected":false},"excerpt":{"rendered":"<p>Learn linked lists in Python with practical code examples, core operations, two-pointer techniques, and common HackerRank and LeetCode problem-solving patterns. Updated August 2026 \u2014 full &hellip; <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"pagelayer_contact_templates":[],"_pagelayer_content":"","footnotes":""},"categories":[35],"tags":[],"class_list":["post-2310","post","type-post","status-publish","format-standard","hentry","category-algorithms"],"acf":[],"_links":{"self":[{"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/posts\/2310","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/comments?post=2310"}],"version-history":[{"count":3,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/posts\/2310\/revisions"}],"predecessor-version":[{"id":2476,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/posts\/2310\/revisions\/2476"}],"wp:attachment":[{"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/media?parent=2310"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/categories?post=2310"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kindsonthegenius.com\/blog\/wp-json\/wp\/v2\/tags?post=2310"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}