How to begin with Competitive Programming? (original) (raw)

Last Updated : 23 Jul, 2025

At the very beginning of competitive programming, barely anyone knew the coding style to be followed. Below is an example to help you understand **how problems are crafted in competitive programming.

competitive-programming

Let us consider below problem statement as an example.

Problem Statement

**Linear Search: Given an integer array and an element x, find if element is present in array or not. If element is present, then print index of its first occurrence. Else print -1.

**Input:

First line contains an integer, the number of test cases 'T'. Each test case should be an integer. Size of the array 'n' in the second line. In the third line, input the integer elements of the array in a single line separated by space. Element X should be input in the fourth line, i.e., after entering the elements of array. Repeat the above steps second line onwards for multiple test cases.

**Output:

Print the output in a separate line returning the index of the element X. If the element is not present, then print -1.

**Constraints:

1 <= T <= 100

1 <= n <= 100

1 <= arr[i] <= 100

Example Input and Output for Your Program

**Input:
2
4
1 2 3 4
3
5
10 90 20 30 40
40
**Output:
2
4

**Explanation:

There are 2 test cases (Note 2 at the beginning of input)
Test Case 1: Input: arr[] = {1, 2, 3, 4},
Element to be searched = 3.
Output: 2
Explanation: 3 is present at index 2.
Test Case 2: Input: arr[] = {10, 90, 20, 30, 40},
Element to be searched = 40.
Output: 4
Explanation: 40 is present at index 4.

C++ `

// A Sample C++ program for beginners with Competitive Programming #include using namespace std;

// This function returns index of element x in arr[] int search(int arr[], int n, int x) { for (int i = 0; i < n; i++) { // Return the index of the element if the element // is found if (arr[i] == x) return i; }

// return -1 if the element is not found
return -1;

}

int main() { // Note that size of arr[] is considered 100 according to // the constraints mentioned in problem statement. int arr[100], x, t, n;

// Input the number of test cases you want to run
cout << "Enter the number of test cases: ";
cin >> t;

// One by one run for all input test cases
while (t--)
{
    // Input the size of the array for the current test case
    cout << "Enter the size of array for this test case: ";
    cin >> n;

    // Input the array elements for the current test case
    cout << "Enter " << n << " elements of array separated by space: ";
    for (int i = 0; i < n; i++)
        cin >> arr[i];

    // Input the element to be searched for the current test case
    cout << "Enter the element to be searched: ";
    cin >> x;

    // Compute and print result
    cout << search(arr, n, x) << "\n";
}
return 0;

}

C

// A Sample C program for beginners with Competitive Programming #include<stdio.h>

// This function returns index of element x in arr[] int search(int arr[], int n, int x) { int i; for (i = 0; i < n; i++) { // Return the index of the element if the element // is found if (arr[i] == x) return i; }

//return -1 if the element is not found
return -1;

}

int main() { // Note that size of arr[] is considered 100 according to // the constraints mentioned in problem statement. int arr[100], x, t, n, i;

// Input the number of test cases you want to run
scanf("%d", &t); 

// One by one run for all input test cases
while (t--)
{
    // Input the size of the array
    scanf("%d", &n); 

    // Input the array
    for (i=0; i<n; i++)
       scanf("%d",&arr[i]);

    // Input the element to be searched
    scanf("%d", &x);

    // Compute and print result
    printf("%d\n", search(arr, n, x));
}
return 0;

}

Java

// A Sample Java program for beginners with Competitive Programming import java.util.; import java.lang.; import java.io.*;

class LinearSearch { // This function returns index of element x in arr[] static int search(int arr[], int n, int x) { for (int i = 0; i < n; i++) { // Return the index of the element if the element // is found if (arr[i] == x) return i; } 

    // return -1 if the element is not found 
    return -1; 
} 

public static void main (String[] args) throws IOException
{ 
    // Note that size of arr[] is considered 100 according to 
    // the constraints mentioned in problem statement. 
    int[] arr = new int[100]; 

    // Using BufferedReader class to take input 
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
    
    int t = Integer.parseInt(br.readLine()); 
    
    // String Buffer to store answer
    StringBuffer sb = new StringBuffer();

    // One by one run for all input test cases 
    while (t > 0) 
    { 
        // Input the size of the array 
        int n = Integer.parseInt(br.readLine()); 

        // to read multiple integers line 
        String line = br.readLine(); 
        String[] strs = line.trim().split("\\s+"); 
        
        // Input the array 
        for (int i = 0; i < n; i++) 
            arr[i] = Integer.parseInt(strs[i]); 

        // Input the element to be searched 
        int x = Integer.parseInt(br.readLine()); 

        // Compute and print result 
        sb.append(search(arr, n, x)+"\n");

        t--; 
    }
    
    System.out.print(sb);
}

}

Python

A Sample Python program for beginners with Competitive Programming

Returns index of x in arr if it is present,

else returns -1

def search(arr, x): n = len(arr) for j in range(0,n): if (x == arr[j]): return j return -1

Input number of test cases

print("Enter the number of test cases: ") t = int(input())

One by one run for all input test cases

for i in range(0,t):

# Input the size of the array for the current test case
print(f"Enter the size of array for test case {i + 1}: ")
n = int(input())

# Input the array elements for the current test case
print(f"Enter {n} elements of array separated by space: ")
arr = list(map(int, input().split()))

# Input the element to be searched for the current test case
print("Enter the element to be searched: ")
x = int(input())

# Print the result of the search operation for the current test case
print(search(arr, x))

# The element can also be searched by the index method
# But you need to handle the exception when the element is not found
# Uncomment the below line to get that working.
# arr.index(x)

C#

using System;

class Program { // This function returns index of element x in arr[] static int Search(int[] arr, int n, int x) { for (int i = 0; i < n; i++) { // Return the index of the element if the element is found if (arr[i] == x) return i; }

    // return -1 if the element is not found
    return -1;
}

static void Main(string[] args)
{
    // Note that size of arr[] is considered 100 according to
    // the constraints mentioned in problem statement.
    int[] arr = new int[100];
    int x, t, n;

    // Input the number of test cases you want to run
    Console.Write("Enter the number of test cases: ");
    if (!int.TryParse(Console.ReadLine(), out t))
    {
        Console.WriteLine("Invalid input. Please enter a valid integer.");
        return;
    }

    // One by one run for all input test cases
    while (t-- > 0)
    {
        // Input the size of the array for the current test case
        Console.Write("Enter the size of array for this test case: ");
        if (!int.TryParse(Console.ReadLine(), out n))
        {
            Console.WriteLine("Invalid input. Please enter a valid integer.");
            continue;
        }

        // Input the array elements for the current test case
        Console.Write($"Enter {n} elements of array separated by space: ");
        string[] input = Console.ReadLine().Split();
        if (input.Length != n)
        {
            Console.WriteLine("Invalid input. Please enter exactly n elements separated by space.");
            continue;
        }
        for (int i = 0; i < n; i++)
        {
            if (!int.TryParse(input[i], out arr[i]))
            {
                Console.WriteLine("Invalid input. Please enter valid integers separated by space.");
                continue;
            }
        }

        // Input the element to be searched for the current test case
        Console.Write("Enter the element to be searched: ");
        if (!int.TryParse(Console.ReadLine(), out x))
        {
            Console.WriteLine("Invalid input. Please enter a valid integer.");
            continue;
        }

        // Compute and print result
        Console.WriteLine(Search(arr, n, x));
    }
}

}

` JavaScript ``

// Function to search for the index of element x in arr[] function search(arr, x) { for (let i = 0; i < arr.length; i++) { // Return the index of the element if found if (arr[i] === x) return i; }

// Return -1 if the element is not found
return -1;

}

// Main function function main() { let t; // Number of test cases console.log("Enter the number of test cases: "); t = parseInt(prompt());

// One by one run for all input test cases
while (t--) {
    let n; // Size of the array
    console.log(`Enter the size of array for test case ${t + 1}: `);
    n = parseInt(prompt());

    let arr = new Array(n); // Array to store elements
    console.log(`Enter ${n} elements of array separated by space: `);
    let elements = prompt().split(' ');

    // Convert input string to integer array
    for (let i = 0; i < n; i++) {
        arr[i] = parseInt(elements[i]);
    }

    let x; // Element to be searched
    console.log("Enter the element to be searched: ");
    x = parseInt(prompt());

    // Compute and print the result
    console.log(`Result for test case <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mrow><mi>t</mi><mo>+</mo><mn>1</mn></mrow><mo>:</mo></mrow><annotation encoding="application/x-tex">{t + 1}: </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7278em;vertical-align:-0.0833em;"></span><span class="mord"><span class="mord mathnormal">t</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mord">1</span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">:</span></span></span></span>{search(arr, x)}`);
}

}

// Calling the main function main();

``

**Common mistakes by beginners

  1. Program should not print any extra character. Writing a statement like printf("Enter value of n") would cause rejection on any platform.
  2. Input and output format specifications must be read carefully. For example, most of the problems expect a new line after every output. So if we don't write printf("\n") or equivalent statement in a loop that runs for all test cases, the program would be rejected.

How to Begin Practice?

You can begin with above problem itself. Try submitting one of the above solutions here. It is recommended solve problems on Practice for cracking any coding interview.
Now you know how to write your first program in Competitive Programming Environment, you can start with School Practice Problems for Competitive Programming or Basic Practice Problems for Competitive Programming.

**Platforms for practicing the Competitive Programming

**Must Read

Conclusion

In conclusion, competitive programming starts with understanding how to read and follow problem statements carefully. As shown in the linear search example, it's important to stick to the exact input and output formats without adding extra prompts or text. Small mistakes like missing a newline or printing unnecessary messages can lead to rejection. Beginners should focus on solving simple problems first to build confidence and learn the structure of coding challenges. Platforms like Codechef, Leetcode, and GeeksForGeeks offer a great place to practice and improve. With regular practice, anyone can develop strong problem-solving and coding skills.