Basic Programs Every Beginner Must Know (LCM, Sum, Factorial)

These are the most important beginner problems asked in interviews and tests.
Let’s understand them with logic + flow + code in 3 languages.

1. Sum of N Numbers

Find the sum from a starting number to an ending number.

Python

output

JAVA

import java.util.Scanner;

public class SumN {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int start = sc.nextInt();
        int end = sc.nextInt();

        int result = 0;

        while (start <= end) {
            result += start;
            start++;
        }

        System.out.println(result);
    }
}

JavaScript

let start = 1;
let end = 10;

let result = 0;

while (start <= end) {
    result += start;
    start++;
}

console.log(result);

2. LCM (Least Common Multiple)

Find the smallest number divisible by both numbers.

Python

output

JAVA

import java.util.Scanner;

public class LCM {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        int b = sc.nextInt();

        int max = (a > b) ? a : b;

        while (true) {
            if (max % a == 0 && max % b == 0) {
                System.out.println(max);
                break;
            }
            max++;
        }
    }
}

JavaScript

let a = 30;
let b = 35;

let max = a > b ? a : b;

while (true) {
    if (max % a === 0 && max % b === 0) {
        console.log(max);
        break;
    }
    max++;
}

3. Factorial

Find factorial of a number
5! = 5 × 4 × 3 × 2 × 1 = 120

Python

output

JAVA

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int result = 1;

        while (n > 0) {
            result *= n;
            n--;
        }

        System.out.println(result);
    }
}

JavaScript

let n = 5;
let result = 1;

while (n > 0) {
    result *= n;
    n--;
}

console.log(result);