Day 1 of 100 Days of DSA: Programming Fundamentals - Diving into the Basics

Welcome to the start of my 100 Days of DSA challenge! Today, I tackled five foundational programming problems using Java to strengthen my understanding of basic algorithms and control structures. Here’s a detailed walkthrough of the problems and solutions:

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1. Check if a Number is Even or Odd

To determine if a number is even or odd, we use the modulus operator %. If the number is divisible by 2, it's even; otherwise, it's odd.

Code:

import java.util.*;

public class EvenorOdd {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number:");
        int num = sc.nextInt();
        sc.close();
        if(num%2==0)
            System.out.println("Number is Even");
        else
            System.out.println("Number is Odd");
    }   
}

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2. Find the Factorial of a Number

The factorial of a number ( n ) is the product of all positive integers less than or equal to ( n ). This can be calculated using a loop.

Code:

import java.util.*;

public class Factorial {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number:");
        int num = sc.nextInt();
        int ans = 1;
        sc.close();
        if(num==0 || num==1)
            ans = 1;
        else{
            while(num>1){
                ans*=num;
                num--;
            }
        } 
        System.out.println("Factorial is: "+ans);
    }
}

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3. Print the First n Fibonacci Numbers

The Fibonacci sequence is a series where each number is the sum of the two preceding ones, starting with 0 and 1.

Code:

import java.util.Scanner;

public class Fibonacci {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of Fibonacci terms: ");
        int n = scanner.nextInt();
        int a = 0, b = 1;

        System.out.print("Fibonacci Sequence: ");
        for (int i = 0; i < n; i++) {
            System.out.print(a + " ");
            int next = a + b;
            a = b;
            b = next;
        }
    }
}

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4. Check if a Number is Prime

A prime number is greater than 1 and divisible only by 1 and itself. We check divisors up to the square root of the number.

Code:

import java.util.Scanner;

public class PrimeCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();

        if (number > 1) {
            boolean isPrime = true;
            for (int i = 2; i <= Math.sqrt(number); i++) {
                if (number % i == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                System.out.println(number + " is a Prime number");
            } else {
                System.out.println(number + " is not a Prime number");
            }
        } else {
            System.out.println(number + " is not a Prime number");
        }
    }
}

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5. Reverse a Number

To reverse a number, we repeatedly extract its last digit using the modulus operator and reconstruct it in reverse order.

Code:

import java.util.Scanner;

public class ReverseNumber {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();
        int reversedNumber = 0;

        while (number > 0) {
            int digit = number % 10;
            reversedNumber = reversedNumber * 10 + digit;
            number /= 10;
        }

        System.out.println("Reversed Number is " + reversedNumber);
    }
}

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Reflection

Starting with programming fundamentals builds a strong base for tackling complex problems later. These exercises emphasized logic, loops, and conditionals—essential skills for any programmer. Stay tuned as I level up in this journey of solving Data Structures and Algorithms!

See you tomorrow with Day 2! 🚀