{"id":7479,"date":"2025-07-02T15:06:53","date_gmt":"2025-07-02T09:36:53","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=7479"},"modified":"2025-07-22T21:55:38","modified_gmt":"2025-07-22T16:25:38","slug":"valid-palindrome-approach-2-two-pointers","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/valid-palindrome-approach-2-two-pointers\/","title":{"rendered":"Valid Palindrome | Approach 2 Two Pointers"},"content":{"rendered":"\n<!-- Prism.js CSS and JS -->\n<link\n  href=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/themes\/prism-tomorrow.css\"\n  rel=\"stylesheet\"\n\/>\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/prism.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_code-tabs-container {\n    font-family: \"Segoe UI\", sans-serif !important;\n    max-width: 900px !important;\n    margin: 2rem auto !important;\n    border: 1px solid #ddd !important;\n    border-radius: 8px !important;\n    overflow: hidden !important;\n    background-color: white !important;\n  }\n\n  .wp_blog_code-tabs-header {\n    background: #f7f7f7 !important;\n    display: flex !important;\n    border-bottom: 1px solid #ddd !important;\n  }\n\n  .wp_blog_code-tab-button {\n    flex: 1 !important;\n    padding: 10px 15px !important;\n    border: none !important;\n    background: transparent !important;\n    cursor: pointer !important;\n    font-weight: bold !important;\n    transition: background 0.2s !important;\n    color: #242b33 !important;\n  }\n\n  .wp_blog_code-tab-button.active {\n    background: white !important;\n    border-bottom: 3px solid #0073aa !important;\n  }\n\n  .wp_blog_code-tab-content {\n    display: none !important;\n    padding: 20px !important;\n    background: #242b33 !important;\n  }\n\n  .wp_blog_code-tab-content > pre {\n    background: #242b33 !important;\n  }\n\n  .wp_blog_code-tab-content.active {\n    display: block !important;\n  }\n\n  .wp_blog_code-tab-content pre {\n    margin: 0 !important;\n    overflow-x: auto !important;\n  }\n\n  .wp_blog_explanation {\n    max-width: 900px !important;\n    margin: 2rem auto !important;\n    font-family: \"Segoe UI\", sans-serif !important;\n    line-height: 1.6 !important;\n    background: white !important;\n    color: black !important;\n    padding: 1rem !important;\n    border-radius: 8px !important;\n  }\n\n  .wp_blog_explanation h2 {\n    color: #0073aa !important;\n    font-size: 1.5rem !important;\n    margin-bottom: 0.5rem !important;\n  }\n\n  .wp_blog_explanation code {\n    background: #f1f1f1 !important;\n    padding: 2px 6px !important;\n    border-radius: 4px !important;\n    font-family: monospace !important;\n  }\n\n  .wp_blog_explanation h1,\n  .wp_blog_explanation h2,\n  .wp_blog_explanation h3,\n  .wp_blog_explanation h4,\n  .wp_blog_explanation h5,\n  .wp_blog_explanation h6,\n  .wp_blog_explanation p {\n    margin-top: 10px !important;\n    margin-bottom: 10px !important;\n  }\n<\/style>\n\n\n<div class=\"wp_blog_explanation\">\n    <p>\n      This approach checks if a string is a valid palindrome by using two pointers. It ignores non-alphanumeric characters and is case-insensitive. A valid palindrome reads the same forward and backward after filtering.\n    <\/p>\n  \n    <h2>Steps<\/h2>\n    <ul>\n      <li>Convert the string to lowercase to simplify comparison.<\/li>\n      <li>Initialize two pointers: one at the start and one at the end of the string.<\/li>\n      <li>Move both pointers toward the center while skipping non-alphanumeric characters.<\/li>\n      <li>Compare the characters at both pointers.<\/li>\n      <li>If they differ, return <code>false<\/code>. If they match, continue moving.<\/li>\n      <li>If all valid characters match, return <code>true<\/code>.<\/li>\n    <\/ul>\n  \n    <h2>Dry Run<\/h2>\n    <p><strong>Input 1:<\/strong> <code>\"race a car\"<\/code><\/p>\n    <ol>\n      <li>Lowercase: <code>\"race a car\"<\/code><\/li>\n      <li>Compare &#8216;r&#8217; and &#8216;r&#8217; \u2192 match<\/li>\n      <li>Compare &#8216;a&#8217; and &#8216;a&#8217; \u2192 match<\/li>\n      <li>Compare &#8216;c&#8217; and &#8216;c&#8217; \u2192 match<\/li>\n      <li>Compare &#8216;e&#8217; and &#8216;a&#8217; \u2192 mismatch<\/li>\n      <li>Return <code>false<\/code><\/li>\n    <\/ol>\n  \n    <p><strong>Input 2:<\/strong> <code>\"A man, a plan, a canal: Panama\"<\/code><\/p>\n    <ol>\n      <li>Lowercase: <code>\"a man, a plan, a canal: panama\"<\/code><\/li>\n      <li>All alphanumeric characters match from start and end<\/li>\n      <li>Return <code>true<\/code><\/li>\n    <\/ol>\n  \n    <h2>Time &#038; Space Complexity<\/h2>\n    <ul>\n      <li><strong>Time Complexity:<\/strong> O(n), where n is the length of the string<\/li>\n      <li><strong>Space Complexity:<\/strong> O(1), since no extra space is used beyond pointers<\/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=\"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=\"java\">Java<\/button>\n      <button class=\"wp_blog_code-tab-button\" data-lang=\"py\">Python<\/button>\n    <\/div>\n  \n    <!-- JavaScript -->\n    <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n      <pre><code class=\"language-javascript\">\n  var isPalindrome = function(s) {\n    s = s.toLowerCase();\n    let i = 0;\n    let j = s.length - 1;\n    while (i < j) {\n        if (!s[i].match(\/[a-z0-9]\/i)) {\n            ++i;\n        }\n        else if (!s[j].match(\/[a-z0-9]\/i)) {\n            --j;\n        }\n        else if (s[i] === s[j]) {\n            ++i;\n            --j;\n        }\n        else {\n            return false;\n        }\n    }\n    return true;\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\">\n  #include &lt;iostream&gt;\n  #include &lt;cctype&gt;\n  using namespace std;\n  \n  bool isPalindrome(string s) {\n      int i = 0, j = s.length() - 1;\n      while (i < j) {\n          if (!isalnum(s[i])) {\n              i++;\n          } else if (!isalnum(s[j])) {\n              j--;\n          } else if (tolower(s[i]) == tolower(s[j])) {\n              i++;\n              j--;\n          } else {\n              return false;\n          }\n      }\n      return true;\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\">\n  #include &lt;stdio.h&gt;\n  #include &lt;ctype.h&gt;\n  #include &lt;string.h&gt;\n  \n  int isPalindrome(char* s) {\n      int i = 0, j = strlen(s) - 1;\n      while (i < j) {\n          if (!isalnum(s[i])) {\n              i++;\n          } else if (!isalnum(s[j])) {\n              j--;\n          } else if (tolower(s[i]) == tolower(s[j])) {\n              i++;\n              j--;\n          } else {\n              return 0;\n          }\n      }\n      return 1;\n  }\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\">\n  public class Solution {\n      public boolean isPalindrome(String s) {\n          int i = 0, j = s.length() - 1;\n          while (i < j) {\n              char ci = s.charAt(i);\n              char cj = s.charAt(j);\n              if (!Character.isLetterOrDigit(ci)) {\n                  i++;\n              } else if (!Character.isLetterOrDigit(cj)) {\n                  j--;\n              } else if (Character.toLowerCase(ci) == Character.toLowerCase(cj)) {\n                  i++;\n                  j--;\n              } else {\n                  return false;\n              }\n          }\n          return true;\n      }\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\">\n  def isPalindrome(s: str) -> bool:\n      i, j = 0, len(s) - 1\n      while i < j:\n          if not s[i].isalnum():\n              i += 1\n          elif not s[j].isalnum():\n              j -= 1\n          elif s[i].lower() == s[j].lower():\n              i += 1\n              j -= 1\n          else:\n              return False\n      return True\n      <\/code><\/pre>\n    <\/div>\n  <\/div>\n  \n\n\n\n<a href=\"https:\/\/leetcode.com\/problems\/two-sum\/description\/\" target=\"blank\"\n  >Solve this problem.<\/a\n>\n<script>\n  document.addEventListener(\"DOMContentLoaded\", function () {\n    const buttons = document.querySelectorAll(\".wp_blog_code-tab-button\");\n    const contents = document.querySelectorAll(\".wp_blog_code-tab-content\");\n\n    buttons.forEach((button) => {\n      button.addEventListener(\"click\", () => {\n        const lang = button.getAttribute(\"data-lang\");\n\n        buttons.forEach((btn) => btn.classList.remove(\"active\"));\n        button.classList.add(\"active\");\n\n        contents.forEach((content) => {\n          content.classList.toggle(\n            \"active\",\n            content.getAttribute(\"data-lang\") === lang\n          );\n        });\n      });\n    });\n  });\n<\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>This approach checks if a string is a valid palindrome by using two pointers. It ignores non-alphanumeric characters and is case-insensitive. A valid palindrome reads the same forward and backward after filtering. Steps Convert the string to lowercase to simplify comparison. Initialize two pointers: one at the start and one at the end of the<\/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":[322,176,175,174,172,173],"tags":[],"class_list":{"0":"post-7479","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-algorithms-and-data-structures","7":"category-csharp","8":"category-cplusplus","9":"category-java","10":"category-javascript","11":"category-python"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/7479","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=7479"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/7479\/revisions"}],"predecessor-version":[{"id":7491,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/7479\/revisions\/7491"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=7479"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=7479"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=7479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}