{"id":10063,"date":"2025-09-11T15:01:50","date_gmt":"2025-09-11T09:31:50","guid":{"rendered":"https:\/\/namastedev.com\/blog\/?p=10063"},"modified":"2025-09-11T15:08:22","modified_gmt":"2025-09-11T09:38:22","slug":"lemonade-change","status":"publish","type":"post","link":"https:\/\/namastedev.com\/blog\/lemonade-change\/","title":{"rendered":"Lemonade Change"},"content":{"rendered":"\n<!-- Greedy Assign Lemonde: 4 -->\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        At a lemonade stand, each lemonade costs <code>$5<\/code>. Customers are standing in a queue to buy from you and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a <code>$5<\/code> , <code>$10<\/code>, or <code>$20<\/code> bill. You must provide the correct change to each customer so that the net transaction is that the customer pays <code>$5<\/code>. \n    <\/p>\n\n    <p>\n       <strong>Note that you do not have any change in hand at first.<\/strong>\n    <\/p>\n\n    <p>\n        Given an integer array <code>bills<\/code> where <code>bills[i]<\/code> is the bill the <code>i<sup>th<\/sup><\/code> customer pays, return <code>true<\/code> <i>if you can provide every customer with the correct change, or <code>false<\/code> otherwise<\/i>.\n    <\/p>\n\n    <h3>Example 1:<\/h2>\n    <p><strong>Input:<\/strong> bills = [5,5,5,10,20]\n<\/p>\n    <p><strong>Output:<\/strong> true<\/p>\n    <p><strong>Explanation:<\/strong><\/p>\n    <strong>\n        <ul>\n            <li>From the first 3 customers, we collect three $5 bills in order.<\/li>\n            <li>From the fourth customer, we collect a $10 bill and give back a $5.<\/li>\n            <li>From the fifth customer, we give a $10 bill and a $5 bill.<\/li>\n            <li>Since all customers got correct change, we output true.<\/li>\n        <\/ul>\n    <\/strong>\n\n    <h3>Example 2:<\/h3>\n    <p><strong>Input: <\/strong>bills = [5,5,10,10,20]<\/p>\n    <p><strong>Output: <\/strong>false<\/p>\n    <p><strong>Explanation: <\/strong><\/p>\n    <strong>\n    <ul>\n        <li>From the first two customers in order, we collect two $5 bills.<\/li>\n        <li>For the next two customers in order, we collect a $10 bill and give back a $5 bill.<\/li>\n        <li>For the last customer, we can not give the change of $15 back because we only have two $10 bills.<\/li>\n        <li>Since not every customer received the correct change, the answer is false.<\/li>\n    <\/ul>\n    <\/strong>\n\n    <h3>Constraints<\/h3>\n    <ul>\n        <li><code>1 <= bills.length <= 10<sup>5<\/sup><\/code><\/li>\n        <li><code>bills[i] is either 5, 10, or 20.<\/code><\/li>\n    <\/ul>\n<h2>Approach:<\/h2>\n    <ul>\n        <li>Maintain a <strong>wallet<\/strong> to track count of <code>$5<\/code> and <code>$10<\/code> bills.<\/li>\n        <li><strong>Iterate<\/strong> over each customer\u2019s bill:\n            <ul>\n                <li>If bill is <code>$5<\/code> \u2192 add to wallet.<\/li>\n                <li>If bill is <code>$10<\/code> \u2192 give one <code>$5<\/code> as change and add one <code>$10<\/code>.<\/li>\n                <li>If bill is <code>$20<\/code> \u2192\n                    <ul>\n                        <li>Prefer giving one <code>$10<\/code> + one <code>$5<\/code> if possible.<\/li>\n                        <li>Otherwise, give three <code>$5<\/code>.<\/li>\n                    <\/ul>\n                <\/li>\n            <\/ul>\n        <\/li>\n        <li>After each transaction, if wallet runs out of required bills (negative count), return <code>false<\/code>.<\/li>\n        <li>If all <strong>transactions succeed<\/strong>, <strong>return<\/strong> <code>true<\/code>.<\/li>\n    <\/ul>\n\n    <h2>Time &#038; 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    \n<h2>Dry Run<\/h2> <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);\"> <p><strong>Input:<\/strong> <code>bills = [5, 5, 5, 10, 20]<\/code><\/p> <pre style=\"white-space: pre-wrap; background: var(--code-bg); padding: 1rem; border-radius: 8px; overflow-x: auto; color: var(--code-text);\">\n\nStep 1: Initialize\nwallet = [0, 0] \/\/ [count of $5, count of $10]\nStep 2: Process each bill\ni = 0 \u2192 bill = 5\nAdd one $5 \u2192 wallet = [1, 0]\ni = 1 \u2192 bill = 5\nAdd one $5 \u2192 wallet = [2, 0]\ni = 2 \u2192 bill = 5\nAdd one $5 \u2192 wallet = [3, 0]\ni = 3 \u2192 bill = 10\nGive back one $5, keep one $10\nwallet = [2, 1]\ni = 4 \u2192 bill = 20\nPrefer $10 + $5 if possible\nUse one $10 and one $5 \u2192 wallet = [1, 0]\nStep 3: Validation\nAt each step, wallet[0] (number of $5) never goes negative.\nStep 4: End\nReturn true\n<\/pre> <p><strong>Output:<\/strong> <code>Result: true<\/code><\/p> <\/div>\n\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 lemonadeChange = function(bills) {\n    let wallet = [0, 0]; \n    for (let i = 0; i < bills.length; ++i) {\n        if (bills[i] === 5) {\n            wallet[0]++;\n        } else if (bills[i] === 10) {\n            wallet[1]++;\n            wallet[0]--;\n        } else { \/\/ bill is 20\n            if (wallet[1] > 0) {\n                wallet[1]--;\n                wallet[0]--;\n            } else {\n                wallet[0] -= 3;\n            }\n        }\n        if (wallet[0] < 0) {\n            return false;\n        }\n    }\n    return true;\n}; <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"py\">\n      <pre><code class=\"language-python\">\ndef lemonadeChange(bills):\n    wallet = [0, 0]  \n    for b in bills:\n        if b == 5:\n            wallet[0] += 1\n        elif b == 10:\n            wallet[1] += 1\n            wallet[0] -= 1\n        else:  # b == 20\n            if wallet[1] > 0:\n                wallet[1] -= 1\n                wallet[0] -= 1\n            else:\n                wallet[0] -= 3\n        if wallet[0] < 0:\n            return False\n    return True\n      <\/code><\/pre>\n    <\/div>\n\n    <div class=\"wp_blog_code-tab-content\" data-lang=\"java\">\n      <pre><code class=\"language-java\">\npublic class Solution {\n    public boolean lemonadeChange(int[] bills) {\n        int[] wallet = new int[2]; \/\/ wallet[0] = $5, wallet[1] = $10\n        for (int i = 0; i < bills.length; i++) {\n            int b = bills[i];\n            if (b == 5) {\n                wallet[0]++;\n            } else if (b == 10) {\n                wallet[1]++;\n                wallet[0]--;\n            } else { \/\/ b == 20\n                if (wallet[1] > 0) {\n                    wallet[1]--;\n                    wallet[0]--;\n                } else {\n                    wallet[0] = wallet[0] - 3;\n                }\n            }\n            if (wallet[0] < 0) return false;\n        }\n        return true;\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;\nusing namespace std;\nbool lemonadeChange(vector<int>& bills) {\n    int wallet[2] = {0, 0};\n    for (int b : bills) {\n        if (b == 5) {\n            wallet[0]++;\n        } else if (b == 10) {\n            wallet[1]++;\n            wallet[0]--;\n        } else { \/\/ b == 20\n            if (wallet[1] > 0) {\n                wallet[1]--;\n                wallet[0]--;\n            } else {\n                wallet[0] -= 3;\n            }\n        }\n        if (wallet[0] < 0) return false;\n    }\n    return true;\n}\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;stdbool.h&gt;\n\nbool lemonadeChange(int* bills, int billsSize) {\n    int wallet[2] = {0, 0}; \n    for (int i = 0; i < billsSize; ++i) {\n        int b = bills[i];\n        if (b == 5) {\n            wallet[0]++;\n        } else if (b == 10) {\n            wallet[1]++;\n            wallet[0]--;\n        } else { \/\/ b == 20\n            if (wallet[1] > 0) {\n                wallet[1]--;\n                wallet[0]--;\n            } else {\n                wallet[0] -= 3;\n            }\n        }\n        if (wallet[0] < 0) return false;\n    }\n    return true;\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 class Solution {\n    public bool LemonadeChange(int[] bills) {\n        int[] wallet = new int[2];\n        for (int i = 0; i < bills.Length; i++) {\n            int b = bills[i];\n            if (b == 5) {\n                wallet[0]++;\n            } else if (b == 10) {\n                wallet[1]++;\n                wallet[0]--;\n            } else { \/\/ b == 20\n                if (wallet[1] > 0) {\n                    wallet[1]--;\n                    wallet[0]--;\n                } else {\n                    wallet[0] -= 3;\n                }\n            }\n            if (wallet[0] < 0) return false;\n        }\n        return true;\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\") ? \"\u2600\ufe0f\" : \"\ud83c\udf19\";\n  });\n});\n<\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>\ud83c\udf19 Problem Statement: At a lemonade stand, each lemonade costs $5. Customers are standing in a queue to buy from you and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a $5 , $10, or $20 bill. You must provide 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":[210,322,260,176,175,211,810,174,172,173],"tags":[],"class_list":["post-10063","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-dsa","category-java","category-javascript","category-python"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10063","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=10063"}],"version-history":[{"count":3,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10063\/revisions"}],"predecessor-version":[{"id":10067,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/posts\/10063\/revisions\/10067"}],"wp:attachment":[{"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/media?parent=10063"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/categories?post=10063"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/namastedev.com\/blog\/wp-json\/wp\/v2\/tags?post=10063"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}