{"id":10048,"date":"2025-09-09T15:06:36","date_gmt":"2025-09-09T09:36:36","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=10048"},"modified":"2025-09-09T15:47:37","modified_gmt":"2025-09-09T10:17:37","slug":"find-peak-in-a-mountain-array_","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/find-peak-in-a-mountain-array_\/","title":{"rendered":"Find Peak in a Mountain Array"},"content":{"rendered":"\n\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_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\n  <div class=\"wp_blog_explanation\">\n    <h2>Problem Statement:<\/h2>\n   \n    <p>\n        This <strong>algorithm finds the peak element<\/strong> in a mountain array using <strong>binary search<\/strong>. A mountain array increases to a peak and then decreases.\n    <\/p>\n\n    <h2>Approach:<\/h2>\n    <ul>\n        <li>Initialize <code>l = 0<\/code> and <code>r = arr.length - 1<\/code>.<\/li>\n        <li><strong>Use binary search:<\/strong><\/li>\n        <li>If <code>arr[m + 1] > arr[m]<\/code>, peak is to the <code>right \u2192 l = m + 1<\/code>.<\/li>\n        <li><strong>Else<\/strong> peak is at <code>m<\/code> or to the <code>left \u2192 r = m<\/code>.<\/li>\n        <li>When loop ends, <code>l (or r)<\/code> is the peak index.<\/li>\n    <\/ul>\n\n    <h2>Time &#038; Space Complexity:<\/h2>\n    <p><strong>Time Complexity:<\/strong> O(logn)<\/p>\n    <p><strong>Space Complexity:<\/strong> O(1)<\/p>\n\n    \n<h2>Dry Run<\/h2>\n<div style=\"background: var(--light-bg); border-left: 4px solid var(--primary); padding: 1rem; border-radius: var(--tab-radius); margin: 1rem 0; color: var(--text-dark);\">\n  <p><strong>Input:<\/strong> <code>arr = [1, 3, 5, 6, 4, 2]<\/code><\/p>\n  <pre style=\"white-space: pre-wrap; background: var(--code-bg); padding: 1rem; border-radius: 8px; overflow-x: auto; color: var(--code-text);\">\n\nInitial:\nl = 0, r = 5\n\n--- While Loop Execution ---\n\nLoop 1:\nm = 0 + Math.floor((5 - 0) \/ 2) = 2\narr[m] = 5, arr[m+1] = 6\nCondition: arr[m+1] > arr[m] \u2192 6 > 5 \u2192 true\nl = m + 1 = 3\n\nLoop 2:\nl = 3, r = 5\nm = 3 + Math.floor((5 - 3) \/ 2) = 4\narr[m] = 4, arr[m+1] = 2\nCondition: arr[m+1] > arr[m] \u2192 2 > 4 \u2192 false\nr = m = 4\n\nLoop 3:\nl = 3, r = 4\nm = 3 + Math.floor((4 - 3) \/ 2) = 3\narr[m] = 6, arr[m+1] = 4\nCondition: arr[m+1] > arr[m] \u2192 4 > 6 \u2192 false\nr = m = 3\n\nExit Condition:\nl = 3, r = 3 \u2192 loop ends\n\n--- Final Result ---\nReturn r = 3\nPeak element index = 3 (value = 6)\n  <\/pre>\n  <p><strong>Output:<\/strong> <code>Result: 3<\/code><\/p>\n<\/div>\n\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    <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n      <pre><code class=\"language-javascript\">\nvar peakIndexInMountainArray = function(arr) {\n    let l = 0;\n    let r = arr.length - 1;\n    while (l < r) {\n        let m = l + Math.floor((r - l) \/ 2);\n        if (arr[m + 1] > arr[m]) {\n            l = m + 1;\n        } else {\n            r = m;\n        }\n    }\n    return r;\n};\n      <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n      <pre><code class=\"language-python\">\ndef peakIndexInMountainArray(arr):\n    l, r = 0, len(arr) - 1\n    while l < r:\n        m = l + (r - l) \/\/ 2\n        if arr[m + 1] > arr[m]:\n            l = m + 1\n        else:\n            r = m\n    return r\n      <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n      <pre><code class=\"language-java\">\npublic int peakIndexInMountainArray(int[] arr) {\n    int l = 0, r = arr.length - 1;\n    while (l < r) {\n        int m = l + (r - l) \/ 2;\n        if (arr[m + 1] > arr[m]) {\n            l = m + 1;\n        } else {\n            r = m;\n        }\n    }\n    return r;\n}\n      <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"cpp\">\n      <pre><code class=\"language-cpp\">\n<!-- #include &lt;iostream&gt; -->\nint peakIndexInMountainArray(vector& arr) {\n    int l = 0, r = arr.size() - 1;\n    while (l < r) {\n        int m = l + (r - l) \/ 2;\n        if (arr[m + 1] > arr[m]) {\n            l = m + 1;\n        } else {\n            r = m;\n        }\n    }\n    return r;\n}\n<\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"c\">\n      <pre><code class=\"language-c\">\n<!-- #include &lt;stdio.h&gt; -->\nint peakIndexInMountainArray(int* arr, int arrSize) {\n    int l = 0, r = arrSize - 1;\n    while (l < r) {\n        int m = l + (r - l) \/ 2;\n        if (arr[m + 1] > arr[m]) {\n            l = m + 1;\n        } else {\n            r = m;\n        }\n    }\n    return r;\n}\n      <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n      <pre><code class=\"language-csharp\">\npublic int PeakIndexInMountainArray(int[] arr) {\n    int l = 0, r = arr.Length - 1;\n    while (l < r) {\n        int m = l + (r - l) \/ 2;\n        if (arr[m + 1] > arr[m]) {\n            l = m + 1;\n        } else {\n            r = m;\n        }\n    }\n    return r;\n}\n      <\/code><\/pre>\n    <\/div>\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","protected":false},"excerpt":{"rendered":"<p>\ud83c\udf19 Problem Statement: This algorithm finds the peak element in a mountain array using binary search. A mountain array increases to a peak and then decreases. Approach: Initialize l = 0 and r = arr.length &#8211; 1. Use binary search: If arr[m + 1] > arr[m], peak is to the right \u2192 l = m<\/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":[210,322,260,176,175,211,811,810,174,172,173],"tags":[],"class_list":["post-10048","post","type-post","status-publish","format-standard","category-algorithms","category-algorithms-and-data-structures","category-c-c-plus-plus","category-csharp","category-cplusplus","category-data-structures","category-data-structures-and-algorithms","category-dsa","category-java","category-javascript","category-python"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10048","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=10048"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10048\/revisions"}],"predecessor-version":[{"id":10054,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10048\/revisions\/10054"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=10048"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=10048"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=10048"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}