What is an Algorithm?

An algorithm is a step-by-step procedure used to solve a problem or complete a specific task. In programming, an algorithm describes the logical steps that a computer program should follow to produce the correct output.

In simple words, an algorithm is a clear plan for solving a problem. Before writing code, programmers often create an algorithm to understand what needs to be done, what input is required, what processing is needed, and what output should be produced.

A program is written in a programming language, but an algorithm is language-independent. This means the same algorithm can be converted into Java, Python, C, C++, JavaScript, PHP, C#, or any other programming language.

Easy Real-Life Example

In programming, the same idea applies. A programmer writes a series of logical steps so that the computer can solve the problem correctly.

Why Do We Need Algorithms?

Algorithms are needed because computers cannot solve problems automatically without instructions. A computer follows the steps given by the programmer. If the steps are correct, the output will be correct. If the steps are wrong, the output may be wrong.

Characteristics of a Good Algorithm

A good algorithm should be clear, finite, correct, and effective. If an algorithm is confusing or incomplete, it becomes difficult to convert it into code.

Basic Structure of an Algorithm

Most beginner algorithms follow the Input, Process, Output model. First, the algorithm accepts input, then processes the input, and finally produces output.

For example, in a program to calculate total price, the price and quantity are inputs, multiplication is the process, and total price is the output.

Algorithm vs Program

An algorithm and a program are closely related, but they are not the same. An algorithm is the plan, while a program is the implementation of that plan in a programming language.

Algorithm vs Pseudocode vs Flowchart

Algorithms can be represented in different ways. The most common ways are natural language steps, pseudocode, and flowcharts.

Steps to Write an Algorithm

To write a good algorithm, students should understand the problem first and then write the solution step by step.

Example 1: Algorithm to Add Two Numbers

Problem Statement

Algorithm

Pseudocode

START
INPUT number1
INPUT number2
SET sum = number1 + number2
DISPLAY sum
END

Java Code

public class Main {
    public static void main(String[] args) {
        int number1 = 10;
        int number2 = 20;

        int sum = number1 + number2;

        System.out.println("Sum: " + sum);
    }
}

Output

Sum: 30

Example 2: Algorithm to Check Even or Odd

Problem Statement

Algorithm

Pseudocode

START
INPUT number
IF number MOD 2 == 0 THEN
    DISPLAY "Even"
ELSE
    DISPLAY "Odd"
END IF
END

Java Code

public class Main {
    public static void main(String[] args) {
        int number = 8;

        if (number % 2 == 0) {
            System.out.println("Even");
        } else {
            System.out.println("Odd");
        }
    }
}

Example 3: Algorithm to Find the Largest of Three Numbers

Problem Statement

Algorithm

Pseudocode

START
INPUT A, B, C
SET max = A

IF B > max THEN
    SET max = B
END IF

IF C > max THEN
    SET max = C
END IF

DISPLAY max
END

Java Code

public class Main {
    public static void main(String[] args) {
        int a = 10;
        int b = 25;
        int c = 15;

        int max = a;

        if (b > max) {
            max = b;
        }

        if (c > max) {
            max = c;
        }

        System.out.println("Largest Number: " + max);
    }
}

Output

Largest Number: 25

Types of Algorithms

Algorithms can be classified based on the type of problem they solve and the method they use. Beginners do not need to master all types at once, but they should know the common categories.

Three Basic Programming Concepts in Algorithms

Many algorithms are built using three basic programming concepts: sequence, selection, and repetition.

Example 4: Algorithm to Print Numbers from 1 to 5

Algorithm

Pseudocode

START
SET counter = 1

WHILE counter <= 5 DO
    DISPLAY counter
    SET counter = counter + 1
END WHILE

END

Java Code

public class Main {
    public static void main(String[] args) {
        int counter = 1;

        while (counter <= 5) {
            System.out.println(counter);
            counter++;
        }
    }
}

Algorithm Efficiency

Algorithm efficiency means how well an algorithm uses time and memory. A solution should not only be correct; it should also be efficient when working with large amounts of data.

Time Complexity and Space Complexity

Time complexity describes how the running time of an algorithm grows as input size increases. Space complexity describes how much memory an algorithm needs.

Dry Run of an Algorithm

A dry run means manually checking an algorithm step by step using sample input values. It helps students understand how variables change and whether the logic is correct.

Dry Run Example

Algorithm: Add two numbers.

Prerequisites Before Learning Algorithms

Algorithms can be learned by beginners, but some basic programming knowledge makes learning easier.

Common Beginner Mistakes

Practice Activity: Write an Algorithm

This activity helps students practice writing algorithms before coding.

Problem Statement

IPO Analysis

Algorithm

Pseudocode

START
INPUT length
INPUT width
SET area = length * width
DISPLAY area
END

Java Solution

public class Main {
    public static void main(String[] args) {
        int length = 10;
        int width = 5;

        int area = length * width;

        System.out.println("Area of Rectangle: " + area);
    }
}

Mini Quiz

Interview Questions on Algorithm

Quick Summary