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chapter 4: stacks
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‎src/04-stack/01-using-stack-class.js‎

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// src/04-stack/01-using-stack-class.js
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const Stack = require('./stack');
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// import { Stack } from './stack'; // or './stack.js' if you are using ES modules
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const stack = new Stack();
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console.log(stack.isEmpty()); // true
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stack.push({action: 'typing', text: 'S'});
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stack.push({action: 'typing', text: 't'});
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console.log(stack.peek()); // { action: 'typing', text: 't' }
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console.log(stack.size); // 2
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stack.push({action: 'typing', text: 'a'});
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stack.push({action: 'typing', text: 'c'});
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stack.push({action: 'typing', text: 'k'});
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console.log(stack.size); // 5
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console.log(stack.isEmpty()); // false
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// removing two elements from the stack
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stack.pop();
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stack.pop();
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console.log(stack.size); // 3
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console.log(stack.peek()); // { action: 'typing', text: 'a' }
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// toString
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console.log(stack.toString());
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// to see the output of this file use the command: node src/04-stack/01-using-stack-class.js

‎src/04-stack/01-using-stack-class.ts‎

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// src/04-stack/01-using-stack-class.ts
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import Stack from './stack';
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enum Action {
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TYPE = 'typing'
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}
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interface EditorAction {
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action: Action;
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text: string;
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}
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const stack = new Stack<EditorAction>();
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console.log(stack.isEmpty()); // true
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console.log(stack.peek()); // undefined
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stack.push({action: Action.TYPE, text: 'S'});
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stack.push({action: Action.TYPE, text: 't'});
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console.log(stack.peek()); // { action: 'typing', text: 't' }
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console.log(stack.size); // 2
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stack.push({action: Action.TYPE, text: 'a'});
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stack.push({action: Action.TYPE, text: 'c'});
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stack.push({action: Action.TYPE, text: 'k'});
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console.log(stack.size); // 5
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console.log(stack.isEmpty()); // false
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// removing two elements from the stack
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stack.pop();
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stack.pop();
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console.log(stack.size); // 3
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console.log(stack.peek()); // { action: 'typing', text: 'a' }
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// toString
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console.log(stack.toString());
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// to see the output of this file use the command: npx ts-node src/04-stack/01-using-stack-class.ts

‎src/04-stack/02-using-stack-object-class.js‎

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// src/04-stack/02-using-stack-object-class.js
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const Stack = require('./stack-object');
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// import { Stack } from './stack-object'; // or './stack-object.js' if you are using ES modules
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const stack = new Stack();
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console.log(stack.isEmpty()); // true
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console.log(stack.peek()); // undefined
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stack.push({action: 'typing', text: 'S'});
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stack.push({action: 'typing', text: 't'});
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// internal object representation
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// #items = {
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// 0: { action: 'typing', text: 'S' },
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// 1: { action: 'typing', text: 't' }}
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// };
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// #count = 2;
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console.log(stack.peek()); // { action: 'typing', text: 't' }
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console.log(stack.size); // 2
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stack.push({action: 'typing', text: 'a'});
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stack.push({action: 'typing', text: 'c'});
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stack.push({action: 'typing', text: 'k'});
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console.log(stack.size); // 5
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console.log(stack.isEmpty()); // false
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// removing two elements from the stack
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stack.pop();
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stack.pop();
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console.log(stack.size); // 3
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console.log(stack.peek()); // { action: 'typing', text: 'a' }
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// toString
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console.log(stack);
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// to see the output of this file use the command: node src/04-stack/02-using-stack-object-class.js

‎src/04-stack/02-using-stack-object-class.ts‎

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// src/04-stack/02-using-stack-object-class.ts
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import Stack from './stack-object';
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interface EditorAction {
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action: string;
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text: string;
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}
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const stack = new Stack<EditorAction>();
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console.log(stack.isEmpty()); // true
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console.log(stack.peek()); // undefined
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stack.push({action: 'typing', text: 'S'});
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stack.push({action: 'typing', text: 't'});
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// internal object representation
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// #items = {
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// 0: { action: 'typing', text: 'S' },
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// 1: { action: 'typing', text: 't' }}
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// };
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// #count = 2;
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console.log(stack.peek()); // { action: 'typing', text: 't' }
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console.log(stack.size); // 2
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stack.push({action: 'typing', text: 'a'});
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stack.push({action: 'typing', text: 'c'});
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stack.push({action: 'typing', text: 'k'});
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console.log(stack.size); // 5
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console.log(stack.isEmpty()); // false
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// removing two elements from the stack
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stack.pop();
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stack.pop();
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console.log(stack.size); // 3
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console.log(stack.peek()); // { action: 'typing', text: 'a' }
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// toString
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console.log(stack);
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// to see the output of this file use the command: npx ts-node src/04-stack/02-using-stack-object-class.js

‎src/04-stack/03-base-converter-examples.js‎

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// src/04-stack/03-base-converter-examples.js
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const decimalToBinary = require('./decimal-to-binary');
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const converters = require('./decimal-to-base');
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// Decimal to binary
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console.log(decimalToBinary(0)); // 0
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console.log(decimalToBinary(1)); // 1
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console.log(decimalToBinary(2)); // 10
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console.log(decimalToBinary(13)); // 1101
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console.log(decimalToBinary(233)); // 11101001
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console.log(decimalToBinary(10)); // 1010
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console.log(decimalToBinary(1000)); // 1111101000
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// Decimal to base
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console.log(converters.decimalToBase(100345, 2)); // 11000011111111001
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console.log(converters.decimalToBase(100345, 8)); // 303771
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console.log(converters.decimalToBase(100345, 16)); // 187F9
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console.log(converters.decimalToBase(100345, 35)); // 2BW0
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// Decimal to base 64
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console.log(converters.decimalToBase64(100345, 64)); // Yf5=
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// to see the output of this file use the command: node src/04-stack/03-base-converter-examples.js

‎src/04-stack/decimal-to-base.js‎

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// src/04-stack/decimal-to-base.js
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const Stack = require('./stack');
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/**
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* Converts a decimal number to a given base
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* @param {number} decimalNumber - decimal number to be converted
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* @param {number} base - base to convert the decimal number to
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* @returns {string} base representation of the decimal number
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*/
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function decimalToBase(decimalNumber, base) {
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if (base < 2 || base > 36) {
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throw new Error('Base must be between 2 and 36');
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}
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const digits = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'; // Digits for base 36
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const remainderStack = new Stack();
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let baseString = '';
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while (decimalNumber > 0) {
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const remainder = Math.floor(decimalNumber % base);
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remainderStack.push(remainder);
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decimalNumber = Math.floor(decimalNumber / base);
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}
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while (!remainderStack.isEmpty()) {
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baseString += digits[remainderStack.pop()]; // Use digit mapping
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}
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return baseString;
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}
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/**
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* Converts a decimal number to a given base
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* @param {number} decimalNumber - decimal number to be converted (between 2 and 36 or 64)
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* @param {number} base - base to convert the decimal number to
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* @returns {string} base representation of the decimal number
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*/
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function decimalToBase64(decimalNumber, base) {
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if (base < 2 || (base > 36 && base !== 64)) {
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throw new Error('Base must be between 2 and 36 or 64');
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}
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const digits = base === 64 ?
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'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/' :
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'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
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const remainderStack = new Stack();
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let baseString = '';
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while (decimalNumber > 0) {
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const remainder = Math.floor(decimalNumber % base);
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remainderStack.push(remainder);
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decimalNumber = Math.floor(decimalNumber / base);
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}
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while (!remainderStack.isEmpty()) {
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baseString += digits[remainderStack.pop()];
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}
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// Handle padding for Base64 (if necessary)
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/* Base64 encodes data in groups of 3 bytes (24 bits).
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Each group is represented by four Base64 characters (6 bits per character).
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If the input data length isn't divisible by 3, padding characters (=) are added to the end of the output
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to ensure that the total length is a multiple of 4.
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This is important for proper decoding of the Base64 string back to its original data. */
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if (base === 64) {
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while (baseString.length % 4 !== 0) {
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baseString += '=';
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}
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}
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return baseString;
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}
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module.exports = { decimalToBase, decimalToBase64 };

‎src/04-stack/decimal-to-binary.js‎

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// src/04-stack/decimal-to-binary.js
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const Stack = require('./stack');
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/**
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* Converts a decimal number to binary
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* @param {number} decimalNumber - decimal number to be converted
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* @returns {string} binary representation of the decimal number
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*/
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function decimalToBinary(decimalNumber) {
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const remainderStack = new Stack();
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let binaryString = '';
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if (decimalNumber === 0) {
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return '0';
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}
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while (decimalNumber > 0) { // {1}
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const remainder = Math.floor(decimalNumber % 2); // {2}
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remainderStack.push(remainder); // {3}
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decimalNumber = Math.floor(decimalNumber / 2); // {4}
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}
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while (!remainderStack.isEmpty()) { // {5}
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binaryString += remainderStack.pop().toString();
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}
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return binaryString;
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}
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module.exports = decimalToBinary;

‎src/04-stack/leetcode/min-stack.ts‎

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// time complexity: O(1)
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// space complexity: O(n)
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// optimized solution
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class MinStack2 {
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stack: number[] = [];
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min: number = +Infinity;
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push(val: number): void {
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this.min = Math.min(val, this.min);
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this.stack.push(val);
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}
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pop(): void {
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const val = this.stack.pop();
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if (this.min === val) this.min = Math.min(...this.stack);
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}
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top(): number {
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return this.stack[this.stack.length - 1];
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}
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getMin(): number {
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return this.min;
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}
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}
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class MinStack3 {
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private stack: number[];
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private minStack: number[];
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constructor() {
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this.stack = [];
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this.minStack = [];
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}
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push(val: number): void {
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this.stack.push(val);
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if (this.minStack.length === 0) this.minStack.push(val);
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else {
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const currentMin = this.minStack[this.minStack.length - 1];
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this.minStack.push(val < currentMin ? val : currentMin);
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}
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}
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pop(): void {
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this.stack.pop();
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this.minStack.pop();
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}
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top(): number {
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return this.stack[this.stack.length - 1];
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}
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getMin(): number {
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return this.minStack[this.minStack.length - 1];
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}
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}
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// to see the output of this file use the command: node src/04-stack/leetcode/min-stack.ts

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