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Print numbers 1 to N using Indirect recursion
  • Difficulty Level : Medium
  • Last Updated : 20 Jan, 2020

Given a number N, we need to print numbers from 1 to N with out direct recursion, loops, labels. Basically we need to insert in above code snippet so that it can be able to print numbers from 1 to N?

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#include <stdio.h>
#define N 20;
int main()
   // Your code goes Here.
}

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Examples :

Input  : 10
Output : 1 2 3 4 5 6 7 8 9 10

Input  : 5
Output : 1 2 3 4 5

We have already discussed solutions in below posts :
Print 1 to 100 in C++, without loop and recursion
How will you print numbers from 1 to 100 without using loop?

Here’s the code that can print the numbers from 1 to 100 with out direct recursion, loops and labels. The code uses indirect recursion.

C

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// C program to print from 1 to N using
// indirect recursion/
#include<stdio.h>
  
// We can avoid use of these using references
#define N 20;
int n = 1;
  
// Prints n, increments n and calls fun1()
void fun1()
{
    if (n <= N)
    {
        printf("%d", n);
        n++;
        fun2();
    }
    else
        return;
}
  
// Prints n, increments n and calls fun2()
void fun2()
{
    if (n <= N)
    {
        printf("%d", n);
        n++;
        fun1();
    }
    else
        return;
}
  
// Driver Program
int main(void)
{
    fun1();
    return 0;
}

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Java

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// Java program to print from 1 to N using
// indirect recursion
class GFG 
{
    // We can avoid use of these using references
    static final int N = 20;
    static int n = 1;
  
    // Prints n, increments n and calls fun1()
    static void fun1() 
    {
        if (n <= N) 
        {
            System.out.printf("%d ", n);
            n++;
            fun2();
        }
        else
        {
            return;
        }
    }
  
    // Prints n, increments n and calls fun2()
    static void fun2() 
    {
        if (n <= N)
        {
            System.out.printf("%d ", n);
            n++;
            fun1();
        
        else 
        {
            return;
        }
    }
  
    // Driver Program
    public static void main(String[] args) 
    {
        fun1();
    }
}
  
// This code is contributed by Rajput-Ji

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Python3

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# Python program to prfrom 1 to N using
# indirect recursion
  
# We can avoid use of these using references
N = 20;
n = 1;
  
# Prints n, increments n and calls fun1()
def fun1():
    global N, n;
    if (n <= N):
        print(n, end = " ");
        n += 1;
        fun2();
    else:
        return;
  
# Prints n, increments n and calls fun2()
def fun2():
    global N, n;
    if (n <= N):
        print(n, end = " ");
        n += 1;
        fun1();
    else:
        return;
  
# Driver Program
if __name__ == '__main__':
  
    fun1();
  
# This code is contributed by 29AjayKumar

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C#

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// C# program to print from 1 to N using
// indirect recursion
using System;
  
class GFG 
{
    // We can avoid use of these using references
    static readonly int N = 20;
    static int n = 1;
  
    // Prints n, increments n and calls fun1()
    static void fun1() 
    {
        if (n <= N) 
        {
            Console.Write("{0} ", n);
            n++;
            fun2();
        }
        else
        {
            return;
        }
    }
  
    // Prints n, increments n and calls fun2()
    static void fun2() 
    {
        if (n <= N)
        {
            Console.Write("{0} ", n);
            n++;
            fun1();
        
        else
        {
            return;
        }
    }
  
    // Driver Code
    public static void Main(String[] args) 
    {
        fun1();
    }
}
  
// This code is contributed by Rajput-Ji

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PHP

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<?php
// PHP program to print 
// from 1 to N using 
// indirect recursion
  
// We can avoid use of
// these using references
$N = 20;
$n = 1;
  
// Prints n, increments 
// n and calls fun1()
function fun1()
{
    global $N;
    global $n;
  
    if ($n <= $N)
    {
        echo $n, " ";
        $n++;
        fun2();
    }
    else
        return;
}
  
// Prints n, increments
// n and calls fun2()
function fun2()
{
    global $N;
    global $n;
    if ($n <= $N)
    {
        echo $n, " ";
        $n++;
        fun1();
    }
    else
        return;
}
  
// Driver Code
fun1();
  
// This code is contributed 
// by m_kit
?>

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Output :



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 

How This works?:
In above Above program, we just used two functions. One calls others and other one calls previous one, therefore indirect recursion.

Exercise :
Modify the above program to use N as a parameter instead of making it global.

This article is contributed by Umamaheswararao Tumma of Jntuh college of Engineering Hyderabad. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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