{"id":12237,"date":"2026-05-10T15:38:09","date_gmt":"2026-05-10T10:08:09","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=12237"},"modified":"2026-05-10T15:39:48","modified_gmt":"2026-05-10T10:09:48","slug":"rabin-karp-algorithm","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/rabin-karp-algorithm\/","title":{"rendered":"Rabin Karp Algorithm"},"content":{"rendered":"\n\n<link\n    href=\"https:\/\/cdn.jsdelivr.net\/npm\/prismjs@1.29.0\/themes\/prism-tomorrow.min.css\"\n    rel=\"stylesheet\"\n\/>\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_theme {\n  --primary: #E58C32;\n  --secondary: #030302;\n  --light-bg: #fef9f4;\n  --text-dark: #2d2d2d;\n  --tab-radius: 12px;\n  --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);\n  --code-bg: #001f3f;\n  --code-text: #d4f1ff;\n}\n\n.wp_blog_container {\n  font-family: 'Segoe UI', sans-serif;\n  background: var(--light-bg);\n  margin: 0;\n  padding: 0;\n  color: var(--text-dark);\n}\n\n\/* Heading *\/\n.wp_blog_main-heading {\n  text-align: center;\n  font-size: 2.4rem;\n  color: var(--primary);\n  margin-top: 2.5rem;\n  font-weight: bold;\n}\n\n\/* Explanation Card *\/\n.wp_blog_explanation,\n.wp_blog_code-tabs-container {\n  max-width: 940px;\n  margin: 2rem auto;\n  padding: 2rem;\n  background: white;\n  border-radius: var(--tab-radius);\n  box-shadow: var(--shadow);\n}\n\n\/* Text and Visuals *\/\n.wp_blog_explanation h2 {\n  font-size: 1.4rem;\n  color: var(--primary);\n  margin-bottom: 0.5rem;\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}\n\n.wp_blog_explanation code {\n  background: #fef9f4;   \/* light bg instead of dark blue *\/\n  color: #E58C32;        \/* brand orange *\/\n  padding: 3px 6px;\n  border-radius: 4px;\n  font-family: 'Courier New', monospace;\n  font-weight: 600;      \/* optional, makes it pop *\/\n}\n\n.wp_blog_explanation img {\n  max-width: 100%;\n  border-radius: var(--tab-radius);\n  margin-top: 1rem;\n  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.06);\n}\n\n\/* Tab Buttons *\/\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 var(--primary);\n  background: white;\n  color: var(--primary);\n  border-radius: 50px;\n  font-weight: 600;\n  cursor: pointer;\n  transition: all 0.3s ease;\n}\n\n.wp_blog_code-tab-button:hover {\n  background: var(--secondary);\n}\n\n.wp_blog_code-tab-button.active {\n  background: var(--primary);\n  color: white;\n}\n\n\/* Code Content *\/\n.wp_blog_code-tab-content {\n  display: none;\n  background: var(--code-bg);\n  border-radius: var(--tab-radius);\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  background: var(--code-bg);\n  border-radius: var(--tab-radius);\n  color: var(--code-text);\n}\n\n\/* Dark mode variables *\/\n.wp_blog_theme.dark-mode {\n  --light-bg: #121212;\n  --text-dark: #f5f5f5;\n  --shadow: 0 4px 12px rgba(255, 255, 255, 0.08);\n  --code-bg: #1e1e1e;\n  --code-text: #c5f0ff;\n}\n\n.wp_blog_theme.dark-mode .wp_blog_explanation {\n  background: #1e1e1e;\n}\n\n\/* Dark mode code highlight *\/\n.wp_blog_theme.dark-mode .wp_blog_explanation code {\n  background: #333;\n  color: #ffd27f;\n}\n\n.wp_blog_theme {\n  position: relative; \/* makes it the reference for absolute children *\/\n}\n\n.wp_blog_toggle-btn {\n  position: absolute;\n  top: 1rem;\n  right: 1rem;\n  z-index: 9999;\n  padding: 0.5rem 0.8rem;\n  border-radius: 10%;\n  background: var(--primary);\n  color: white;\n  font-weight: bold;\n  cursor: pointer;\n  border: none;\n  box-shadow: var(--shadow);\n  transition: background 0.3s, transform 0.2s;\n}\n\n.wp_blog_toggle-btn:hover {\n  background: #cc772e;\n}\n\n.wp_blog_theme.dark-mode .wp_blog_code-tabs-container {\n  background: #1e1e1e;\n}\n<\/style>\n\n<div class=\"wp_blog_container wp_blog_theme\"> \n      <button id=\"blogNotesThemeToggle\" class=\"wp_blog_toggle-btn\">\ud83c\udf19<\/button>\n    <h1 class=\"wp_blog_main-heading\"><\/h1>\n    <div class=\"wp_blog_explanation\">\n        <h2>Rabin Karp<\/h2>\n        <p>The Rabin\u2013Karp algorithm is a <code>string-searching algorithm<\/code> used to <strong>find a pattern inside a larger text<\/strong>. It\u2019s especially useful when you need to <code>search for multiple patterns<\/code> or do <strong>repeated searches efficiently<\/strong>.<\/p>\n        <p><strong>It uses rolling hashing.<\/strong><\/p>\n\n        <p><strong>text:<\/strong> <code> a b c d b a c d\u2028<\/code><\/p>\n        <p><strong>Pattern Hash: <\/strong><code>7 (4+2+1)<\/code> Add all the values of Hash.<\/p>\n\n        <ul>\n            <li>a = 1<\/li>\n            <li>b = 2<\/li>\n            <li>c = 3<\/li>\n            <li>d = 4<\/li>\n            <li>e = 5<\/li>\n            <li>f = 6<\/li>\n            <li>g = 7<\/li>\n            <li>h = 8<\/li>\n            <li>i = 9<\/li>\n            <li>j = 10<\/li>\n        <\/ul>\n        \n\n        <p>\n            Now, I will proceed with the <strong>testing and create a window with the same pattern and dimensions as the original pattern.\n        <\/strong><\/p>\n        <ul>\n\n            <img decoding=\"async\" src=\"https:\/\/namastedev.com\/blog\/wp-content\/uploads\/2026\/05\/Screenshot-2026-05-10-at-2.09.12-PM.png\" alt=\"\">\n    <li>\n        Now for <strong>a b c<\/strong><br>\n        <code>window hash = 1 + 2 + 3 = 6<\/code><br>\n        Is the <strong>windowHash matching the pattern hash?<\/strong> <code>No <\/code>\u274c<br>\n        a b c is not a valid pattern.\n    <\/li>\n\n    <li>\n        Now, check for <strong>b c d<\/strong><br>\n        <code>window hash = 2 + 3 + 4 = 9<\/code><br>\n        Is the <strong>windowHash matching the pattern hash?<\/strong> <code>No <\/code>\u274c<br>\n        b c d is not a valid pattern.\n    <\/li>\n\n    <li>\n        Now, check for <strong>c d b<\/strong><br>\n        <code>window hash = 3 + 4 + 2 = 9<\/code><br>\n        Is the <strong>windowHash matching the pattern hash?<\/strong> <code>No <\/code> \u274c<br>\n        c d b is not a valid pattern.\n    <\/li>\n\n    <li>\n        Now, check for <strong>d b a<\/strong><br>\n        <code>window hash = 4 + 2 + 1 = 7<\/code><br>\n        Is the <strong>windowHash matching the pattern hash?<\/strong> <code>Yes<\/code> \u2705<br>\n        <code> Now the hash is matching.<\/code>\n    <\/li>\n\n    <li>\n        Now, check each and every character.<br>\n        If the pattern matches, <code>then we can say it\u2019s a valid pattern<\/code>.<br>\n       <strong><code> d b a is a valid pattern<\/code><\/strong>.\n    <\/li>\n<\/ul>\n\n\n<h2>Spurious Hits<\/h2>\n\n<p>\nIn the <strong>Rabin\u2013Karp algorithm<\/strong>, a spurious hit happens when:\nThe hash <code>value of the pattern and the current text window are the same<\/code>,\nbut the actual <strong>strings are different<\/strong>.\nSo the <code>algorithm thinks it found a match based on the hash<\/code>, but after <strong>algorithm thinks it found a match based on the hash<\/strong>, it turns out to be false.\n<\/p>\n<img decoding=\"async\" src=\"https:\/\/namastedev.com\/blog\/wp-content\/uploads\/2026\/05\/Screenshot-2026-05-10-at-2.29.00-PM.png\" alt=\"\">\n\n<p><strong>Note: <code>To reduce spurious hits, we need to use a stronger hash function.\n<\/code><\/strong><\/p>\n\n<h2>How can we calculate a strong hash?<\/h2>\n\n<p><strong> <code>text = a b c d b a c d<\/code><\/strong><\/p>\n\n<p><strong> <code>Pattern = d b a<\/code><\/strong><\/p>\n\n<ul>\n    <li>a = 1<\/li>\n    <li>b = 2<\/li>\n    <li>c = 3<\/li>\n    <li>d = 4<\/li>\n    <li>e = 5<\/li>\n    <li>f = 6<\/li>\n    <li>g = 7<\/li>\n    <li>h = 8<\/li>\n    <li>i = 9<\/li>\n    <li>j = 10<\/li>\n    <li>k = 11<\/li>\n    <li>l = 12<\/li>\n    <li>m = 13<\/li>\n    <li>n = 14<\/li>\n    <li>o = 15<\/li>\n    <li>p = 16<\/li>\n    <li>q = 17<\/li>\n    <li>r = 18<\/li>\n    <li>s = 19<\/li>\n    <li>t = 20<\/li>\n    <li>u = 21<\/li>\n    <li>v = 22<\/li>\n    <li>w = 23<\/li>\n    <li>x = 24<\/li>\n    <li>y = 25<\/li>\n    <li>z = 26<\/li>\n<\/ul>\n\n\n\n<p><strong>StrongHash: <\/strong> \n<code>(10<sup>2<\/sup> x 4) + (10<sup>1<\/sup> x 2) + (10<sup>0<\/sup> x 1)<\/code><\/p>\n\n<p><strong><code>400 + 20 + 1 = 421<\/code><\/strong><\/p>\n\n    <p>\n        In the Rabin\u2013Karp algorithm, <code>256 is commonly used<\/code> as the base because the <code>ASCII character set contains 256<\/code> possible characters. This helps generate stronger and <strong>more unique hash values for efficient string matching.\n    <\/strong><\/p>\n\n\n<p><strong> <code>text = a b c d b a c d<\/code><\/strong><\/p>\n\n<p><strong> <code>Pattern = d b a<\/code><\/strong><\/p>\n\n<p><strong>StrongHash: <\/strong> \n<code>(26<sup>2<\/sup> x 4) + (26<sup>1<\/sup> x 2) + (26<sup>0<\/sup> x 1)<\/code><\/p>\n\n<p><strong><code>2704 + 52 + 1 = 2757<\/code><\/strong><\/p>\n\n<p><code>Using a larger base such as 26 or 256<\/code> does not change the theoretical <code>time complexity of Rabin\u2013Karp<\/code>, but it <strong>reduces hash collisions and spurious hits<\/strong>, making the algorithm more efficient in practice.<\/p>\n<\/div>\n<\/div>\n\n<script>\ndocument.addEventListener(\"DOMContentLoaded\", () => {\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      contents.forEach((content) => content.classList.remove(\"active\"));\n\n      button.classList.add(\"active\");\n      document\n        .querySelector(`.wp_blog_code-tab-content[data-lang=\"${lang}\"]`)\n        .classList.add(\"active\");\n    });\n  });\n\n  const themeToggle = document.getElementById(\"blogNotesThemeToggle\");\n  const themeContainer = document.querySelector(\".wp_blog_theme\");\n\n  themeToggle.addEventListener(\"click\", () => {\n    themeContainer.classList.toggle(\"dark-mode\");\n    themeToggle.textContent =\n      themeContainer.classList.contains(\"dark-mode\") ? \"\u2600\ufe0f\" : \"\ud83c\udf19\";\n  });\n});\n<\/script>\n\n\n","protected":false},"excerpt":{"rendered":"<p>\ud83c\udf19 Rabin Karp The Rabin\u2013Karp algorithm is a string-searching algorithm used to find a pattern inside a larger text. It\u2019s especially useful when you need to search for multiple patterns or do repeated searches efficiently. It uses rolling hashing. text: a b c d b a c d\u2028 Pattern Hash: 7 (4+2+1) Add all the<\/p>\n","protected":false},"author":108,"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":[322,176,175,211,174,172,173],"tags":[],"class_list":["post-12237","post","type-post","status-publish","format-standard","category-algorithms-and-data-structures","category-csharp","category-cplusplus","category-data-structures","category-java","category-javascript","category-python"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/12237","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\/108"}],"replies":[{"embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/comments?post=12237"}],"version-history":[{"count":1,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/12237\/revisions"}],"predecessor-version":[{"id":12238,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/12237\/revisions\/12238"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=12237"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=12237"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=12237"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}