{"id":9725,"date":"2025-08-28T17:18:09","date_gmt":"2025-08-28T11:48:09","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=9725"},"modified":"2025-09-30T12:36:04","modified_gmt":"2025-09-30T07:06:04","slug":"sum-of-odd-numbers-in-array-using-recursion_","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/sum-of-odd-numbers-in-array-using-recursion_\/","title":{"rendered":"Sum of odd numbers in array using Recursion"},"content":{"rendered":"\n<!-- Sum of all numbers in array using Recursion 1 -->\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\n<h1 class=\"wp_blog_main-heading\"><\/h1>\n\n<div class=\"wp_blog_explanation\">\n    <h2>Problem Statement:<\/h2>\n    <p>\n        Write a recursive function sum(n) that calculates the sum of all odd numbers in an array arr up to index n.\n    <\/p>\n    <h2>Example:<\/h2>\n    <p><strong>Input:<\/strong> [5, 2, 6, 1, 3]<\/p>\n    <p><strong>Odd Numbers:<\/strong> 5, 1, 3<\/p>\n    <p><strong>Output:<\/strong> 9<\/p>\n\n\n    <h2>Concepts:<\/h2>\n    <ul>\n        <li><strong>Recursion:<\/strong> Repeatedly check whether <code>arr[n]<\/code> is <strong>odd<\/strong>, and add it only if true <code>true<\/code>.<\/li>\n        <li><strong>Base Case:<\/strong> If n == 0, <code>return arr[0]<\/code> if it\u2019s <strong>odd<\/strong>, otherwise <code>0<\/code>.<\/li>\n        <li><strong>Recursive Case:<\/strong> <code>Return (arr[n] if odd) + sum(n - 1).<\/code><\/li>\n    <\/ul>\n\n\n    <h2>Approach:<\/h2>\n    <ul>\n        <li>Check if <code>arr[n]<\/code> is <strong>odd<\/strong>.<\/li>\n        <li>If <strong>yes<\/strong>, add it to <code>recursive result<\/code> of <code>sum(n-1)<\/code>.<\/li>\n        <li><strong>Else<\/strong>, skip it and continue <strong>recursion<\/strong>.<\/li>\n    <\/ul>\n\n    <h2>Time &#038; Space Complexity:<\/h2>\n    <p><strong>Time Complexity: O(n)<\/strong><\/p>\n    <p><strong>Space Complexity: O(n)<\/strong> <code>recursive call stack<\/code><\/p>\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\">\n            JavaScript\n        <\/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\">\nlet arr = [5, 2, 6, 1, 3];\n\nfunction sum(n) {\n    let isOdd = arr[n] % 2 !== 0;\n    if (n === 0) return isOdd ? arr[0] : 0;\n    return (isOdd ? arr[n] : 0) + sum(n - 1);\n}\nconsole.log(sum(arr.length - 1)); \/\/ Output: 9\n    <\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n        <pre><code class=\"language-python\">\ndef sum_odd(arr, n):\n    is_odd = arr[n] % 2 != 0\n    if n == 0:\n        return arr[0] if is_odd else 0\n    return (arr[n] if is_odd else 0) + sum_odd(arr, n - 1)\n\narr = [5, 2, 6, 1, 3]\nprint(sum_odd(arr, len(arr) - 1))  # Output: 9\n    <\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n        <pre><code class=\"language-java\">\npublic class Main {\n  public static int sum(int[] arr, int n) {\n    boolean isOdd = arr[n] % 2 != 0;\n    if (n == 0) return isOdd ? arr[0] : 0;\n    return (isOdd ? arr[n] : 0) + sum(arr, n - 1);\n  }\n\n  public static void main(String[] args) {\n    int[] arr = {5, 2, 6, 1, 3};\n    System.out.println(sum(arr, arr.length - 1)); \/\/ Output: 9\n  }\n}\n<\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"cpp\">\n        <pre><code class=\"language-cpp\">\n#include &lt;iostream&gt;\nusing namespace std;\n\nint sum(int arr[], int n) {\n  bool isOdd = arr[n] % 2 != 0;\n  if (n == 0) return isOdd ? arr[0] : 0;\n  return (isOdd ? arr[n] : 0) + sum(arr, n - 1);\n}\n\nint main() {\n  int arr[] = {5, 2, 6, 1, 3};\n  int len = sizeof(arr) \/ sizeof(arr[0]);\n  cout << sum(arr, len - 1) << endl; \/\/ Output: 9\n  return 0;\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;\n\nint sum(int arr[], int n) {\n  int isOdd = arr[n] % 2 != 0;\n  if (n == 0) return isOdd ? arr[0] : 0;\n  return (isOdd ? arr[n] : 0) + sum(arr, n - 1);\n}\n\nint main() {\n  int arr[] = {5, 2, 6, 1, 3};\n  int len = sizeof(arr) \/ sizeof(arr[0]);\n  printf(\"%d\\n\", sum(arr, len - 1)); \/\/ Output: 9\n  return 0;\n}\n<\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n        <pre><code class=\"language-csharp\">\nusing System;\n\nclass Program {\n    static int Sum(int[] arr, int n) {\n        bool isOdd = arr[n] % 2 != 0;\n        if (n == 0) return isOdd ? arr[0] : 0;\n        return (isOdd ? arr[n] : 0) + Sum(arr, n - 1);\n    }\n\n    static void Main() {\n        int[] arr = {5, 2, 6, 1, 3};\n        Console.WriteLine(Sum(arr, arr.Length - 1)); \/\/ Output: 9\n    }\n}\n  <\/code><\/pre>\n    <\/div>\n<\/div>\n<\/div>\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","protected":false},"excerpt":{"rendered":"<p>\ud83c\udf19 Problem Statement: Write a recursive function sum(n) that calculates the sum of all odd numbers in an array arr up to index n. Example: Input: [5, 2, 6, 1, 3] Odd Numbers: 5, 1, 3 Output: 9 Concepts: Recursion: Repeatedly check whether arr[n] is odd, and add it only if true true. Base Case:<\/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":[322,260,176,175,211,811,810,174,172,173],"tags":[],"class_list":["post-9725","post","type-post","status-publish","format-standard","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\/9725","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=9725"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9725\/revisions"}],"predecessor-version":[{"id":10173,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9725\/revisions\/10173"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=9725"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=9725"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=9725"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}