Pattern 20

Pattern 20

Beginner Problems Patterns Medium

This problem demonstrates the concept of loops and pattern recognition/matching which is a fundamental aspect in many software applications
In the real-world, pattern generation problems like this are commonly used in computer graphics and game development to generate textures, shapes, or terrain
It is also used in tools like regular expression engines which are widely used in text parsing, syntax highlighting, data validation, and search functionalities which are core to numerous software applications
Interesting fact: Algorithms to generate complex patterns are also pivotal in certain aspects of cryptography and data security

Given an integer n. You need to recreate the pattern given below for any value of N. Let's say for N = 5, the pattern should look like as below:

*        *
**      **
***    ***
****  ****
**********
****  ****
***    ***
**      **
*        *

Print the pattern in the function given to you.

Constraints

1 <= n <= 20

Company Tags

TCS Cognizant Accenture Infosys Capgemini Wipro IBM HCL Tech Mahindra MindTree

Editorial

Approach:

Start by initializing spaces to 2*N - 2. This variable tracks the number of spaces between the two sets of stars in each row, where N is the number of rows.

Use an outer loop (for loop) to iterate from 1 to 2*N- 1. This loop controls the number of rows printed for both the upper and lower halves of the pattern.

Inside the loop, calculate stars: For the first half (when row number <= N), stars starts from 1 and increments with each row. For the second half (when row > N), stars decreases with each row.

Use nested loops to print stars, spaces, the second set of stars, mirroring the first set. After printing stars and spaces for each row, adjust spaces.

If row < N, decrease spaces by 2 to gradually reduce the space between stars as rows progress towards the middle, else, increase spaces by 2 to gradually increase the space as rows move away from the middle.

After completing a row give a line break, to make sure next row gets printed as well.

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    //Function to print pattern20
    void pattern20(int n) {
        // Initialising the spaces.
        int spaces = 2*n-2;
      
        // Outer loop to print the row.
        for(int i = 1; i <= 2*n-1; i++){
          
            // Stars for first half
            int stars = i;
          
            // Stars for the second half.
            if(i > n) stars = 2*n - i;
          
            //For printing the stars
            for(int j = 1; j <= stars; j++){
                cout<<"*";
            }
          
            //For printing the spaces
            for(int j = 1; j <= spaces; j++){
                cout<<" ";
            }
          
            //For printing the stars
            for(int j = 1; j <= stars; j++){
                cout<<"*";
            }
          
            //Give a line break for new row.
            cout<<endl;
            
            if(i<n) spaces -=2;
            else spaces +=2;
        }
    }
};

int main() {
    int N = 5;
    
    //Create an instance of Solution class
    Solution sol;
    
    sol.pattern20(N);
    
    return 0;
}
import java.util.*;
class Solution {
    // Function to print pattern20
    public void pattern20(int n) {
        // Initialising the spaces.
        int spaces = 2*n-2;
        
        // Outer loop to print the row.
        for(int i = 1; i <= 2*n-1; i++){
            // Stars for first half
            int stars = i;
            
            // Stars for the second half.
            if(i > n) stars = 2*n - i;
            
            // For printing the stars
            for(int j = 1; j <= stars; j++){
                System.out.print("*");
            }
            
            // For printing the spaces
            for(int j = 1; j <= spaces; j++){
                System.out.print(" ");
            }
            
            // For printing the stars
            for(int j = 1; j <= stars; j++){
                System.out.print("*");
            }
            
            // Give a line break for new row.
            System.out.println();
            
            if(i < n) spaces -= 2;
            else spaces += 2;
        }
    }

    public static void main(String[] args) {
        int N = 5;
        
        // Create an instance of Solution class
        Solution sol = new Solution();
        
        sol.pattern20(N);
    }
}
class Solution:
    # Function to print pattern20
    def pattern20(self, n):
        # Initialising the spaces.
        spaces = 2 * n - 2
        
        # Outer loop to print the row.
        for i in range(1, 2 * n):
            # Stars for first half
            stars = i
            
            # Stars for the second half.
            if i > n:
                stars = 2 * n - i
            
            # For printing the stars
            print("*" * stars, end="")
            
            # For printing the spaces
            print(" " * spaces, end="")
            
            # For printing the stars
            print("*" * stars, end="")
            
            # Give a line break for new row.
            print()
            
            # Adjust spaces for the next row
            if i < n:
                spaces -= 2
            else:
                spaces += 2

# Main function
if __name__ == "__main__":
    N = 5
    
    # Create an instance of Solution class
    sol = Solution()
    
    sol.pattern20(N)
class Solution {
    // Function to print pattern20
    pattern20(n) {
        // Initialising the spaces.
        let spaces = 2 * n - 2;
        
        // Outer loop to print the row.
        for(let i = 1; i <= 2 * n - 1; i++){
            // Stars for first half
            let stars = i;
            
            // Stars for the second half.
            if(i > n) stars = 2 * n - i;
            
            // For printing the stars
            process.stdout.write("*".repeat(stars));
            
            // For printing the spaces
            process.stdout.write(" ".repeat(spaces));
            
            // For printing the stars
            process.stdout.write("*".repeat(stars));
            
            // Give a line break for new row.
            console.log();
            
            if(i < n) spaces -= 2;
            else spaces += 2;
        }
    }
}
let N = 5;

//Create an instance of Solution class
let sol = new Solution();

sol.pattern20(N);

Complexity Analysis:

Time Complexity : O(N²). The overall complexity will be O(N²), where N is the number of rows.

Space Complexity :O(1). As no extra space is being used to print the patterns.

Code