{"id":9809,"date":"2025-08-30T18:19:31","date_gmt":"2025-08-30T12:49:31","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=9809"},"modified":"2025-09-01T14:59:03","modified_gmt":"2025-09-01T09:29:03","slug":"missing-number_","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/missing-number_\/","title":{"rendered":"Missing Number"},"content":{"rendered":"\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: #f8c291;\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  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auto;\n  background: var(--code-bg);\n  border-radius: var(--tab-radius);\n  color: var(--code-text);\n}\n<\/style>\n\n<div class=\"wp_blog_container wp_blog_theme\"> \n    <h1 class=\"wp_blog_main-heading\"><\/h1>\n    <div class=\"wp_blog_explanation\">\n        <h2>Problem Statement:<\/h2>\n        <p>Given an array nums containing <code>n<\/code> distinct numbers in the range <code>[0, n]<\/code>, return the only number in the range that is missing from the array.<\/p>\n\n                <h2>Examples:<\/h2>\n\n                <h4>Example 1:<\/h4>\n                <p><strong>Input:<\/strong> nums = [3,0,1]<\/p>\n                <p><strong>Output:<\/strong> 2<\/p>\n                <p>\n                  <code>Explanation:<\/code>\n                  n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.\n                <\/p>\n\n                <h4>Example 2:<\/h4>\n                <p><strong>Input:<\/strong> nums = [0,1]<\/p>\n                <p><strong>Output:<\/strong> 2<\/p>\n                  <p>\n                  <code>Explanation:<\/code>\n                  n = 2 since there are 2 numbers, so all numbers are in the range [0,2]. 2 is the missing number in the range since it does not appear in nums.\n                <\/p>\n\n                <h4>Example 3:<\/h4>\n                <p><strong>Input:<\/strong> nums = [9,6,4,2,3,5,7,0,1]<\/p>\n                <p><strong>Output:<\/strong> 8<\/p>\n                  <p>\n                  <code>Explanation:<\/code>\n                  n = 9 since there are 9 numbers, so all numbers are in the range [0,9]. 8 is the missing number in the range since it does not appear in nums.\n                <\/p>\n\n                    <h2>Constraints:<\/h2>\n                    <ul>\n                      <li><code>n == nums.length<\/code><\/li>\n                      <li><code>1 <= n <= 10 <sup>4<\/sup><\/code><\/li>\n                      <li><code>0 <= nums[i] <= n<\/code><\/li>\n                      <li><code>All the numbers of nums are unique.<\/code><\/li>\n                    <\/ul>\n\n                <h2>Approach 1 (Brute-force with sorting and comparison):<\/h2>\n                <ul>\n                    <li><strong>Sort the array<\/strong>.<\/li>\n                    <li>Loop from index <code>1<\/code> to <code>n - 1<\/code><\/li>\n                    <li>If <code>nums[i] != nums[i-1] + 1<\/code>, return <code>nums[i-1] + 1<\/code> as the missing number.<\/li>\n                    <li>If no such mismatch is found:<\/li>\n                    <li>If <code>nums[0] != 0<\/code>, return <code>0<\/code>.<\/li>\n                    <li>Else return <code>n<\/code>.<\/li>\n                <\/ul>\n\n                <h2>Time Complexity:<\/h2>\n                <li>\n                  <p><strong>Time Complexity = O(n log n)<\/strong>\n                Due to sorting the array.\n                  <\/li>\n                <h2>Space Complexity:<\/h2>\n                <li>\n                  <p><strong>Space Complexity = O(1)<\/strong>\n                  Sorting is done in-place, and only a few variables are used.<\/p>\n                <\/li>\n\n                <h2>Dry Run<\/h2>\n                  <div style=\"background: #f9f9f9; border-left: 4px solid var(--primary); padding: 1rem; border-radius: var(--tab-radius); margin: 1rem 0;\">\n                  <p><strong>Input:<\/strong> <code> Input: nums = [4, 2, 1, 0, 5]<\/code><\/p>\n                  <pre style=\"white-space: pre-wrap; background: #fff5ea; padding: 1rem; border-radius: 8px; overflow-x: auto;\">\nAfter Sorting: nums = [0, 1, 2, 4, 5]\n    Check:\n        i = 1 \u2192 1 == 0 + 1\n        i = 2 \u2192 2 == 1 + 1\n        i = 3 \u2192 4 != 2 + 1 \u2192 return 3\n    Final return 3\n  <\/pre>\n                <p><strong>Output:<\/strong> <code>3<\/code><\/p>\n                  <\/div>\n                \n        <h2>Visualisation:<\/h2>\n        <img decoding=\"async\" src=\"https:\/\/namastedev.com\/blog\/wp-content\/uploads\/2025\/07\/Screenshot-2025-07-12-at-9.57.58\u202fAM.png\" alt=\"Stocks\" \/>\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        <!-- JavaScript -->\n        <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n            <pre><code class=\"language-javascript\">\nvar missingNumber = function(nums) {\n      nums.sort((a, b) => a - b);\n      if (nums[0] !== 0) return 0;\n      for (let i = 1; i < nums.length; i++) {\n          if (nums[i] !== nums[i - 1] + 1) {\n              return nums[i - 1] + 1;\n          }\n      } \n      return nums.length;\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\">\nclass Solution:\n      def missingNumber(self, nums):\n          nums.sort()\n  \n          if nums[0] != 0:\n              return 0\n  \n          for i in range(1, len(nums)):\n              if nums[i] != nums[i - 1] + 1:\n                  return nums[i - 1] + 1\n  \n          return len(nums)\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\">\nimport java.util.Arrays;\n  class Solution {\n      public int missingNumber(int[] nums) {\n          Arrays.sort(nums);\n          if (nums[0] != 0) return 0;\n          for (int i = 1; i < nums.length; i++) {\n              if (nums[i] != nums[i - 1] + 1) {\n                  return nums[i - 1] + 1;\n              }\n          }  \n          return nums.length;\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;algorithm&gt;\n  class Solution {\n  public:\n      int missingNumber(vector<int>& nums) {\n          sort(nums.begin(), nums.end());\n  \n          if (nums[0] != 0) return 0;\n  \n          for (int i = 1; i < nums.size(); i++) {\n              if (nums[i] != nums[i - 1] + 1) {\n                  return nums[i - 1] + 1;\n              }\n          }\n  \n          return nums.size();\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 <stdlib.h> -->\n#include &lt;stdlib.h&gt;\n  int compare(const void* a, const void* b) {\n      return (*(int*)a - *(int*)b);\n  }\n  int missingNumber(int* nums, int numsSize) {\n      qsort(nums, numsSize, sizeof(int), compare);\n      if (nums[0] != 0) return 0;\n      for (int i = 1; i < numsSize; i++) {\n          if (nums[i] != nums[i - 1] + 1) {\n              return nums[i - 1] + 1;\n          }\n      }\n      return numsSize;\n  }       <\/code><\/pre>\n        <\/div>\n\n        <!-- C# -->\n        <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n            <pre><code class=\"language-csharp\">\npublic class Solution {\n    public int MissingNumber(int[] nums) {\n        Array.Sort(nums);\n\n        if (nums[0] != 0) return 0;\n\n        for (int i = 1; i < nums.Length; i++) {\n            if (nums[i] != nums[i - 1] + 1) {\n                return nums[i - 1] + 1;\n            }\n        }\n\n        return nums.Length;\n    }\n}       <\/code><\/pre>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div class=\"wp_blog_container wp_blog_theme\"> \n    <h1 class=\"wp_blog_main-heading\"><\/h1>\n    <div class=\"wp_blog_explanation\">\n\n                <h2>Approach 2 (Optimal using Sum Formula):<\/h2>\n                <ul>\n                    <li>The <strong>sum of numbers<\/strong> from <code>0 to n<\/code> is given by the formula:<\/li>\n                    <li><code>total_sum = (n \u00d7 (n + 1)) \/ 2<\/code><\/li>\n                    <li>Steps are as follows:\n                        <ul>\n                            <li><strong>Calculate<\/strong> total_sum using the <code>formula above<\/code>.<\/li>\n                            <li><strong>Calculate the sum<\/strong> of all elements in the <code>input array<\/code>.<\/li>\n                            <li>The <strong>missing<\/strong> number is <code>total_sum - sum_of_array<\/code>.<\/li>\n                        <\/ul>\n                    <\/li>\n                <\/ul>\n\n                <h2>Time Complexity:<\/h2>\n                <li>\n                  <p><strong>Time Complexity = O(n)<\/strong>\n                We traverse the array once to compute the sum.\n                  <\/li>\n                <h2>Space Complexity:<\/h2>\n                <li>\n                  <p><strong>Space Complexity = O(1)<\/strong>\n                  Only a few variables are used, no extra space proportional to input size.<\/p>\n                <\/li>\n\n<h2>Dry Run<\/h2>\n  <div style=\"background: #f9f9f9; border-left: 4px solid var(--primary); padding: 1rem; border-radius: var(--tab-radius); margin: 1rem 0;\">\n  <p><strong>Input:<\/strong> <code>nums = [3, 0, 1]<\/code><\/p>\n  <pre style=\"white-space: pre-wrap; background: #fff5ea; padding: 1rem; border-radius: 8px; overflow-x: auto;\">\nStep 1: n = nums.length = 3\nStep 2: total_sum = (n * (n + 1)) \/ 2 = (3 * 4) \/ 2 = 6\n\nStep 3: sum_of_array = 0\n        num = 3 \u2192 sum_of_array = 3\n        num = 0 \u2192 sum_of_array = 3\n        num = 1 \u2192 sum_of_array = 4\n\nStep 4: return total_sum - sum_of_array = 6 - 4 = 2\n  <\/pre>\n  <p><strong>Output:<\/strong> <code>2<\/code><\/p>\n  <\/div>\n\n                \n        <!-- <h2>Visualisation:<\/h2>\n        <img decoding=\"async\" src=\"https:\/\/namastedev.com\/blog\/wp-content\/uploads\/2025\/08\/Screenshot-2025-08-30-at-6.17.20\u202fPM.png\" alt=\"Stocks\" \/> -->\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        <!-- JavaScript -->\n        <div class=\"wp_blog_code-tab-content active\" data-lang=\"js\">\n            <pre><code class=\"language-javascript\">\n  var missingNumber = function(nums) {\n      let n = nums.length;\n      let total_sum = (n * (n + 1)) \/ 2;\n      let sum_of_array = 0;\n  \n      for (let num of nums) {\n          sum_of_array += num;\n      }\n      return total_sum - sum_of_array;\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 class Solution:\n      def missingNumber(self, nums):\n          n = len(nums)\n          total_sum = n * (n + 1) \/\/ 2\n          sum_of_array = sum(nums)\n          return total_sum - sum_of_array\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\">\nclass Solution {\n      public int missingNumber(int[] nums) {\n          int n = nums.length;\n          int total_sum = n * (n + 1) \/ 2;\n          int sum_of_array = 0;\n  \n          for (int num : nums) {\n              sum_of_array += num;\n          }\n  \n          return total_sum - sum_of_array;\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;algorithm&gt; -->\nclass Solution {\n  public:\n      int missingNumber(vector<int>& nums) {\n          int n = nums.size();\n          int total_sum = n * (n + 1) \/ 2;\n          int sum_of_array = 0;\n  \n          for (int num : nums) {\n              sum_of_array += num;\n          }\n  \n          return total_sum - sum_of_array;\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;stdlib.h&gt; -->\n int missingNumber(int* nums, int numsSize) {\n      int total_sum = numsSize * (numsSize + 1) \/ 2;\n      int sum_of_array = 0;\n  \n      for (int i = 0; i < numsSize; i++) {\n          sum_of_array += nums[i];\n      }\n  \n      return total_sum - sum_of_array;\n  }<\/code><\/pre>\n        <\/div>\n\n        <!-- C# -->\n        <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n            <pre><code class=\"language-csharp\">\nusing System;\n\npublic class Solution {\n    public int MissingNumber(int[] nums) {\n        int n = nums.Length;\n        int total_sum = (n * (n + 1)) \/ 2;\n        int sum_of_array = 0;\n        foreach (int num in nums) {\n            sum_of_array += num;\n        }\n        return total_sum - sum_of_array;\n    }\n}      <\/code><\/pre>\n        <\/div>\n    <\/div>\n<\/div>\n\n<script>\n    document.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) =>\n                    content.classList.remove(\"active\")\n                );\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<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Problem Statement: Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array. Examples: Example 1: Input: nums = [3,0,1] Output: 2 Explanation: n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2<\/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":[210,322,176,175,211,810,174,172,173],"tags":[],"class_list":["post-9809","post","type-post","status-publish","format-standard","category-algorithms","category-algorithms-and-data-structures","category-csharp","category-cplusplus","category-data-structures","category-dsa","category-java","category-javascript","category-python"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9809","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=9809"}],"version-history":[{"count":3,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9809\/revisions"}],"predecessor-version":[{"id":9862,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/9809\/revisions\/9862"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=9809"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=9809"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=9809"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}