{"id":10094,"date":"2025-09-22T20:43:39","date_gmt":"2025-09-22T15:13:39","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=10094"},"modified":"2025-09-23T21:05:30","modified_gmt":"2025-09-23T15:35:30","slug":"gas-station","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/gas-station\/","title":{"rendered":"Gas Station"},"content":{"rendered":"\n\n<!-- merge_7-->\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    <p>\n        There are <code>n<\/code> gas stations along a circular route, where the amount of gas at the <code>i<sup>th<\/sup><\/code> station is <code>gas[i]<\/code>.\n    <\/p>\n    \n    <p>\n        You have a car with an unlimited gas tank and it costs <code>cost[i]<\/code> of gas to travel from the <code>i<sup>th<\/sup><\/code> station to its next <code>(i + 1)<sup>th<\/sup><\/code> station. You begin the journey with an empty tank at one of the gas stations.\n    <\/p>\n\n    <p>\n        Given two integer arrays <code>gas<\/code> and <code>cost<\/code>, return <i>the starting gas station&#8217;s index if you can travel around the circuit once in the clockwise direction, otherwise return <code>-1<\/code>.<\/i> If there exists a solution, it is <strong>guaranteed<\/strong> to be <strong>unique<\/strong>.\n    <\/p>\n\n    <h3>Example 1:<\/h2>\n    <p><strong>Input:<\/strong> gas = [1,2,3,4,5], cost = [3,4,5,1,2]\n<\/p>\n    <p><strong>Output:<\/strong> 3<\/p>\n    <p><strong>Explanation:<\/strong>\n            Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4\n            Travel to station 4. Your tank = 4 &#8211; 1 + 5 = 8\n            Travel to station 0. Your tank = 8 &#8211; 2 + 1 = 7\n            Travel to station 1. Your tank = 7 &#8211; 3 + 2 = 6\n            Travel to station 2. Your tank = 6 &#8211; 4 + 3 = 5\n            Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3.\n            Therefore, return 3 as the starting index.\n    <\/p>\n\n    <h3>Example 2:<\/h3>\n    <p><strong>Input: <\/strong>gas = [2,3,4], cost = [3,4,3]<\/p>\n    <p><strong>Output: <\/strong>-1<\/p>\n    <p><strong>Explanation: <\/strong>You can&#8217;t start at station 0 or 1, as there is not enough gas to travel to the next station.\n    Let&#8217;s start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4\n    Travel to station 0. Your tank = 4 &#8211; 3 + 2 = 3\n    Travel to station 1. Your tank = 3 &#8211; 3 + 3 = 3\n    You cannot travel back to station 2, as it requires 4 unit of gas but you only have 3.\n    Therefore, you can&#8217;t travel around the circuit once no matter where you start.\n<\/p>\n\n    <!-- <h3>Example 3:<\/h3>\n    <p><strong>Input: <\/strong>intervals = [[1,2],[2,3]]<\/p>\n    <p><strong>Output: <\/strong>0<\/p>\n    <p><strong>Explanation: <\/strong>\n       You don't need to remove any of the intervals since they're already non-overlapping.\n    <\/p> -->\n\n    <h3>Constraints<\/h3>\n    <ul>\n        <li><code>n == gas.length == cost.length<\/code><\/li>\n        <li><code>1 <= n <= 10<sup>5<\/sup><\/code><\/li>\n        <li><code>0 <= gas[i], cost[i] <= 10<sup>4<\/sup><\/code><\/li>\n        <li>The input is generated such that the answer is unique.<\/li>\n    <\/ul>\n    \n<h2>Approach:<\/h2>\n   <ul>\n         <li>Calculate the net gain <code>(gas[i] - cost[i])<\/code> at each station.<\/li>\n        <li><strong>Keep two sums<\/strong>:\n            <ul>\n                <li><code>totalGain<\/code>: <strong>total net gain for the whole circuit<\/strong>.<\/li>\n                <li><code>currGain<\/code>: <strong>running sum for the current starting point<\/strong>.<\/li>\n            <\/ul>\n        <\/li>\n         <li>If <code>currGain<\/code> becomes negative, it means you cannot start from the current segment. So, reset <code>currGain = 0<\/code> and set the next station <code>(i+1)<\/code> as the new candidate starting point.<\/li>\n                <li><strong>After the loop:<\/strong>\n            <ul>\n                <li>If <code>totalGain < 0<\/code>, return <code>-1<\/code> (not possible to complete circuit).<\/li>\n                <li>Otherwise, <strong>return ans<\/strong> (the valid starting station index).<\/li>\n            <\/ul>\n        <\/li>\n    <\/ul>\n\n    <h2>Time & Space Complexity:<\/h2>\n    <p><strong>Time Complexity:<\/strong> <code>O(n)<\/code><\/p>\n    <p><strong>Space Complexity:<\/strong> <code>O(1)<\/code><\/p>\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>gas = [1,2,3,4,5], cost = [3,4,5,1,2]<\/code><\/p> \n  \n  <pre style=\"white-space: pre-wrap; background: var(--code-bg); padding: 1rem; border-radius: 8px; overflow-x: auto; color: var(--code-text);\">\n\nStep 0: Start Function: canCompleteCircuit(gas, cost)\ngas = [1,2,3,4,5], cost = [3,4,5,1,2]\ncurrGain = 0, totalGain = 0, ans = 0\n\nIteration (i = 0):\n- gain = gas[0] - cost[0] = 1 - 3 = -2\n- currGain = 0 + (-2) = -2\n- totalGain = 0 + (-2) = -2\n- currGain < 0 \u2192 true \u2192 ans = 0 + 1 = 1, currGain = 0\n\nIteration (i = 1):\n- gain = gas[1] - cost[1] = 2 - 4 = -2\n- currGain = 0 + (-2) = -2\n- totalGain = -2 + (-2) = -4\n- currGain < 0 \u2192 true \u2192 ans = 1 + 1 = 2, currGain = 0\n\nIteration (i = 2):\n- gain = gas[2] - cost[2] = 3 - 5 = -2\n- currGain = 0 + (-2) = -2\n- totalGain = -4 + (-2) = -6\n- currGain < 0 \u2192 true \u2192 ans = 2 + 1 = 3, currGain = 0\n\nIteration (i = 3):\n- gain = gas[3] - cost[3] = 4 - 1 = 3\n- currGain = 0 + 3 = 3\n- totalGain = -6 + 3 = -3\n- currGain < 0 \u2192 false \u2192 ans stays = 3\n\nIteration (i = 4):\n- gain = gas[4] - cost[4] = 5 - 2 = 3\n- currGain = 3 + 3 = 6\n- totalGain = -3 + 3 = 0\n- currGain < 0 \u2192 false \u2192 ans stays = 3\n\nStep 3: End\n- totalGain = 0 \u2192 not < 0\n- return ans = 3\n  <\/pre> \n  \n  <p><strong>Output:<\/strong> <code>3<\/code><\/p> \n<\/div>\n\n<\/div>\n\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 canCompleteCircuit = function (gas, cost) {\n    let currGain = 0;\n    let totalGain = 0;\n    let ans = 0;\n    for (let i = 0; i < gas.length; i++) {\n        let gain = gas[i] - cost[i];\n        currGain += gain;\n        totalGain += gain;\n\n        if (currGain < 0) {\n            ans = i + 1;\n            currGain = 0;\n        }\n    }\n    return totalGain < 0 ? -1 : ans;\n};\n\n<\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n      <pre><code class=\"language-python\">\ndef canCompleteCircuit(gas, cost):\n    currGain = 0\n    totalGain = 0\n    ans = 0\n\n    for i in range(len(gas)):\n        gain = gas[i] - cost[i]\n        currGain += gain\n        totalGain += gain\n        if currGain < 0:\n            ans = i + 1\n            currGain = 0\n\n    return -1 if totalGain < 0 else ans\n      <\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n      <pre><code class=\"language-java\">\npublic class Solution {\n    public int canCompleteCircuit(int[] gas, int[] cost) {\n        long currGain = 0;\n        long totalGain = 0;\n        int ans = 0;\n        int n = gas.length;\n\n        for (int i = 0; i < n; i++) {\n            long gain = (long)gas[i] - (long)cost[i];\n            currGain += gain;\n            totalGain += gain;\n            if (currGain < 0) {\n                ans = i + 1;\n                currGain = 0;\n            }\n        }\n        return (totalGain < 0) ? -1 : ans;\n    }\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;vector&gt; -->\n#include &lt;vector&gt;\n#include &lt;cstdint&gt;\nusing namespace std;\nint canCompleteCircuit(const vector<int>& gas, const vector<int>& cost) {\n    long long currGain = 0;\n    long long totalGain = 0;\n    int ans = 0;\n    int n = gas.size();\n    for (int i = 0; i < n; ++i) {\n        long long gain = (long long)gas[i] - (long long)cost[i];\n        currGain += gain;\n        totalGain += gain;\n        if (currGain < 0) {\n            ans = i + 1;\n            currGain = 0;\n        }\n    }\n    return (totalGain < 0) ? -1 : ans;\n}\n<\/code><\/pre>\n    <\/div>\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"c\">\n      <pre><code class=\"language-c\">\n#include &lt;stdio.h&gt;\nint canCompleteCircuit(int *gas, int *cost, int n) {\n    long long currGain = 0;\n    long long totalGain = 0;\n    int ans = 0;\n\n    for (int i = 0; i < n; ++i) {\n        long long gain = (long long)gas[i] - (long long)cost[i];\n        currGain += gain;\n        totalGain += gain;\n        if (currGain < 0) {\n            ans = i + 1;\n            currGain = 0;\n        }\n    }\n    return (totalGain < 0) ? -1 : ans;\n}\n <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"cs\">\n      <pre><code class=\"language-csharp\">\nusing System;\npublic class Solution {\n    public int CanCompleteCircuit(int[] gas, int[] cost) {\n        long currGain = 0;\n        long totalGain = 0;\n        int ans = 0;\n        int n = gas.Length;\n\n        for (int i = 0; i < n; i++) {\n            long gain = (long)gas[i] - (long)cost[i];\n            currGain += gain;\n            totalGain += gain;\n            if (currGain < 0) {\n                ans = i + 1;\n                currGain = 0;\n            }\n        }\n        return (totalGain < 0) ? -1 : ans;\n    }\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\") ? 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You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey<\/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-10094","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\/10094","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=10094"}],"version-history":[{"count":2,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10094\/revisions"}],"predecessor-version":[{"id":10105,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10094\/revisions\/10105"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=10094"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=10094"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=10094"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}