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Commit b4d028b

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chapter 9: recursion
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// src/09-recursion/01-intro-recursion.js
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// To understand recursion, one must first understand recursion
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const readline = require('readline').createInterface({
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input: process.stdin,
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output: process.stdout
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});
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function understandRecursion() {
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readline.question('Do you understand recursion? (y/n) ', (answer) => {
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if (answer.toLowerCase() === 'y') { // Base case
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console.log("Excellent! You've grasped recursion.");
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readline.close(); // Exit the program
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} else {
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console.log("Let's try again...");
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understandRecursion(); // Recursive call
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}
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});
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}
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understandRecursion();
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// to see the output of this file use the command: node src/09-recursion/01-intro-recursion.js

‎src/09-recursion/02-factorial.js‎

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// src/09-recursion/02-factorial.js
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// iterative approach
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function factorialIterative(number) {
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if (number < 0) {
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return undefined;
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}
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let total = 1;
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for (let n = number; n > 1; n--) {
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total *= n;
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}
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return total;
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}
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console.log('5! =',factorialIterative(5)); // 5! = 120
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// recursive approach
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function factorial(number) {
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// console.trace();
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if (number < 0) { return undefined; }
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if (number === 1 || number === 0) { // base case
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return 1;
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}
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return number * factorial(number - 1);
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}
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console.log('Recursive 5! =',factorial(5)); // Recursive 5! = 120
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// to see the output of this file use the command: node src/09-recursion/02-factorial.js

‎src/09-recursion/03-callstack.js‎

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// src/09-recursion/03-callstack.js
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// stack overflow
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let count = 0;
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function recursiveFn() {
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count++;
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recursiveFn();
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}
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try {
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recursiveFn();
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} catch (ex) {
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console.log('count = ' + count + ' error: ' + ex);
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}
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// to see the output of this file use the command: node src/09-recursion/03-callstack.js

‎src/09-recursion/04-fibonacci.js‎

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// src/09-recursion/04-fibonacci.js
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// iterative approach
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function fibonacciIterative(n) {
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if (n < 0) {
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throw new Error('Input must be a non-negative integer');
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}
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if (n < 2) { return n; }
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let prevPrev = 0;
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let prev = 1;
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let current;
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for (let i = 2; i <= n; i++) { // n >= 2
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current = prev + prevPrev; // f(n-1) + f(n-2)
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prevPrev = prev;
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prev = current;
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}
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return current;
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}
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console.log('fibonacciIterative(2)', fibonacciIterative(2)); // 1
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console.log('fibonacciIterative(3)', fibonacciIterative(3)); // 2
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console.log('fibonacciIterative(4)', fibonacciIterative(4)); // 3
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console.log('fibonacciIterative(5)', fibonacciIterative(5)); // 5
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// recursive approach
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function fibonacci(n) {
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if (n < 0) {
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throw new Error('Input must be a non-negative integer');
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}
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if (n < 2) { return n; } // base case
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return fibonacci(n - 1) + fibonacci(n - 2); // recursive case
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}
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console.log('fibonacci(5)', fibonacci(5)); // 5
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// memoization approach
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function fibonacciMemoization(n) {
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if (n < 0) {
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throw new Error('Input must be a non-negative integer');
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}
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const memo = [0, 1];
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const fibonacci = (n) => {
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if (memo[n] != null) return memo[n];
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return memo[n] = fibonacci(n - 1) + fibonacci(n - 2);
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};
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return fibonacci(n);
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}
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console.log('fibonacciMemoization(5)', fibonacciMemoization(5)); // 5
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// to see the output of this file use the command: node src/09-recursion/04-fibonacci.js
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// https://leetcode.com/problems/fibonacci-number/description/
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function fib(n: number): number {
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if (n < 2) { return n; }
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let prevPrev = 0;
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let prev = 1;
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let current;
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for (let i = 2; i <= n; i++) { // n >= 2
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current = prev + prevPrev; // f(n-1) + f(n-2)
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prevPrev = prev;
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prev = current;
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}
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return current;
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};
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// https://leetcode.com/problems/power-of-two/
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// function isPowerOfTwo(n: number): boolean {
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// if (n <= 0) {
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// return false;
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// }
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// return (n & (n - 1)) === 0;
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// }
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// Time complexity: O(1)
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// Space complexity: O(1)
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// Test cases
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// recursive solution
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function isPowerOfTwo(n: number): boolean {
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if (n <= 0) { // edge case for negative numbers
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return false;
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}
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if (n % 2 !== 0) { // edge case for odd numbers
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return false;
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}
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if (n === 1) { // base case
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return true;
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}
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return isPowerOfTwo(n / 2);
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}
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// Time complexity: O(log n)
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// Space complexity: O(log n)
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// Test cases
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console.log(isPowerOfTwo(1)); // true
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console.log(isPowerOfTwo(16)); // true
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console.log(isPowerOfTwo(3)); // false
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console.log(isPowerOfTwo(4)); // true
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console.log(isPowerOfTwo(5)); // false
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console.log(isPowerOfTwo(0)); // false
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console.log(isPowerOfTwo(-1)); // false

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