Program to print double headed arrow pattern

Given an integer N which is the number of rows, the task is to draw the number pattern in the shape of a double headed arrow.

Prerequisite: The pattern is a grow and shrink type pattern and hence basic knowledge to execute loops is required to understand the topic and the code in any language. The geometric shape can be visualized as-

Examples:

Input: R = 7
Output:   
                  1
               2 1 1 2
            3 2 1   1 2 3
         4 3 2 1     1 2 3 4
            3 2 1   1 2 3
               2 1 1 2
                  1

Input: R = 9
Output:
                       1
                    2 1 1 2
                 3 2 1   1 2 3
              4 3 2 1     1 2 3 4
           5 4 3 2 1       1 2 3 4 5
              4 3 2 1     1 2 3 4
                 3 2 1   1 2 3
                    2 1 1 2
                       1

Approach:

  1. In the given example, N=7 and the number of ROWS is 7.
  2. VERTICALLY, the pattern GROWS till ROW=N/2 and SHRINKS afterwards.
  3. ROW 1 has 4 ” “(SPACE) characters and then a value.
  4. The number of SPACE characters decreases whereas NUMERALS increase in count in each successive row.
  5. Also, note that the 1st value of the number placed in each row is the same as the number of the row.
  6. Also HORIZONTALLY the pattern has NUMERALS, then SPACES and NUMERALS afterwards.

Below is the implementation of the above approach:



C++

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// C++ implementation of the approach
#include <iostream>
using namespace std;
  
// Function to print the requried pattern
void drawPattern(int N)
{
    int n = N;
    int row = 1;
  
    // 'nst' is the number of values
    int nst = 1;
  
    // 'nsp' is the number of spaces
    int nsp1 = n - 1;
    int nsp2 = -1;
    int val1 = row;
    int val2 = 1;
  
    while (row <= n) {
  
        // Here spaces are printed
        // 'csp' is the count of spaces
        int csp1 = 1;
        while (csp1 <= nsp1) {
            cout << " "
                 << " ";
            csp1 = csp1 + 1;
        }
  
        // Now, values are printed
        // 'cst' is the count of stars
        int cst1 = 1;
        while (cst1 <= nst) {
            cout << val1 << " ";
            val1 = val1 - 1;
            cst1 = cst1 + 1;
        }
  
        // Again spaces have to be printed
        int csp2 = 1;
        while (csp2 <= nsp2) {
            cout << " "
                 << " ";
            csp2 = csp2 + 1;
        }
  
        // Again values have to be printed
        if (row != 1 && row != n) {
            int cst2 = 1;
            while (cst2 <= nst) {
                cout << val2 << " ";
                val2 = val2 + 1;
                cst2 = cst2 + 1;
            }
        }
        cout << endl;
  
        // Move to the next row
        if (row <= n / 2) {
            nst = nst + 1;
            nsp1 = nsp1 - 2;
            nsp2 = nsp2 + 2;
            val1 = row + 1;
            val2 = 1;
        }
        else {
            nst = nst - 1;
            nsp1 = nsp1 + 2;
            nsp2 = nsp2 - 2;
            val1 = n - row;
            val2 = 1;
        }
        row = row + 1;
    }
}
  
// Driver code
int main()
{
    // Number of rows
    int N = 7;
  
    drawPattern(N);
  
    return 0;
}

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Java

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// Java implementation of the approach
class GFG {
  
    // Function to print the requried pattern
    static void drawPattern(int N)
    {
        int n = N;
        int row = 1;
  
        // 'nst' is the number of values
        int nst = 1;
  
        // 'nsp' is the number of spaces
        int nsp1 = n - 1;
        int nsp2 = -1;
        int val1 = row;
        int val2 = 1;
  
        while (row <= n) {
  
            // Here spaces are printed
            // 'csp' is the count of spaces
            int csp1 = 1;
            while (csp1 <= nsp1) {
                System.out.print("  ");
                csp1 = csp1 + 1;
            }
  
            // Now, values are printed
            // 'cst' is the count of stars
            int cst1 = 1;
            while (cst1 <= nst) {
                System.out.print(val1 + " ");
                val1 = val1 - 1;
                cst1 = cst1 + 1;
            }
  
            // Again spaces have to be printed
            int csp2 = 1;
            while (csp2 <= nsp2) {
                System.out.print("  ");
                csp2 = csp2 + 1;
            }
  
            // Again values have to be printed
            if (row != 1 && row != n) {
                int cst2 = 1;
                while (cst2 <= nst) {
                    System.out.print(val2 + " ");
                    val2 = val2 + 1;
                    cst2 = cst2 + 1;
                }
            }
            System.out.println();
  
            // Move to the next row
            if (row <= n / 2) {
                nst = nst + 1;
                nsp1 = nsp1 - 2;
                nsp2 = nsp2 + 2;
                val1 = row + 1;
                val2 = 1;
            }
            else {
                nst = nst - 1;
                nsp1 = nsp1 + 2;
                nsp2 = nsp2 - 2;
                val1 = n - row;
                val2 = 1;
            }
            row = row + 1;
        }
    }
  
    // Driver code
    public static void main(String args[])
    {
        // Number of rows
        int N = 7;
  
        drawPattern(N);
    }
}

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Python3

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# Python3 implementation of the approach 
  
# Function to print the requried pattern 
def drawPattern(N) : 
  
    n = N; 
    row = 1
  
    # 'nst' is the number of values 
    nst = 1
  
    # 'nsp' is the number of spaces 
    nsp1 = n - 1
    nsp2 = -1
    val1 = row; 
    val2 = 1
  
    while (row <= n) :
  
        # Here spaces are printed 
        # 'csp' is the count of spaces 
        csp1 = 1
        while (csp1 <= nsp1) :
            print(" ",end= " ");
            csp1 = csp1 + 1
  
        # Now, values are printed 
        # 'cst' is the count of stars 
        cst1 = 1
        while (cst1 <= nst) :
            print(val1,end = " "); 
            val1 = val1 - 1
            cst1 = cst1 + 1
  
        # Again spaces have to be printed 
        csp2 = 1
        while (csp2 <= nsp2) :
            print(" ",end = " "); 
            csp2 = csp2 + 1
  
        # Again values have to be printed 
        if (row != 1 and row != n) :
            cst2 = 1
              
            while (cst2 <= nst) :
                print(val2,end = " "); 
                val2 = val2 + 1
                cst2 = cst2 + 1
          
        print()
  
        # Move to the next row 
        if (row <= n // 2) :
            nst = nst + 1
            nsp1 = nsp1 - 2
            nsp2 = nsp2 + 2
            val1 = row + 1
            val2 = 1
  
        else :
            nst = nst - 1
            nsp1 = nsp1 + 2
            nsp2 = nsp2 - 2
            val1 = n - row; 
            val2 = 1
          
        row = row + 1
  
# Driver code 
if __name__ == "__main__"
  
    # Number of rows 
    N = 7
  
    drawPattern(N); 
  
# This code is contributed by AnkitRai01

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C#

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// C# implementation of the approach
using System;
  
class GFG 
{
  
    // Function to print the requried pattern
    static void drawPattern(int N)
    {
        int n = N;
        int row = 1;
  
        // 'nst' is the number of values
        int nst = 1;
  
        // 'nsp' is the number of spaces
        int nsp1 = n - 1;
        int nsp2 = -1;
        int val1 = row;
        int val2 = 1;
  
        while (row <= n) 
        {
  
            // Here spaces are printed
            // 'csp' is the count of spaces
            int csp1 = 1;
            while (csp1 <= nsp1)
            {
                Console.Write(" ");
                csp1 = csp1 + 1;
            }
  
            // Now, values are printed
            // 'cst' is the count of stars
            int cst1 = 1;
            while (cst1 <= nst) 
            {
                Console.Write(val1 + " ");
                val1 = val1 - 1;
                cst1 = cst1 + 1;
            }
  
            // Again spaces have to be printed
            int csp2 = 1;
            while (csp2 <= nsp2) 
            {
                Console.Write(" ");
                csp2 = csp2 + 1;
            }
  
            // Again values have to be printed
            if (row != 1 && row != n)
            {
                int cst2 = 1;
                while (cst2 <= nst) 
                {
                    Console.Write(val2 + " ");
                    val2 = val2 + 1;
                    cst2 = cst2 + 1;
                }
            }
            Console.WriteLine();
  
            // Move to the next row
            if (row <= n / 2)
            {
                nst = nst + 1;
                nsp1 = nsp1 - 2;
                nsp2 = nsp2 + 2;
                val1 = row + 1;
                val2 = 1;
            }
            else 
            {
                nst = nst - 1;
                nsp1 = nsp1 + 2;
                nsp2 = nsp2 - 2;
                val1 = n - row;
                val2 = 1;
            }
            row = row + 1;
        }
    }
  
    // Driver code
    public static void Main()
    {
        // Number of rows
        int N = 7;
  
        drawPattern(N);
    }
}
  
// This code is contributed by AnkitRai01

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Output:

            1 
        2 1   1 2 
    3 2 1       1 2 3 
4 3 2 1           1 2 3 4 
    3 2 1       1 2 3 
        2 1   1 2 
            1

Time Complexity: O(N2)
Space Complexity: O(1)

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