Practice Questions for Recursion | Set 4
Last Updated :
21 Aug, 2022
Question 1
Predict the output of the following program.
C++
#include <iostream>
using namespace std;
void fun(int x)
{
if(x > 0)
{
fun(--x);
cout << x <<" ";
fun(--x);
}
}
int main()
{
int a = 4;
fun(a);
return 0;
}
|
C
#include<stdio.h>
void fun(int x)
{
if(x > 0)
{
fun(--x);
printf("%d\t", x);
fun(--x);
}
}
int main()
{
int a = 4;
fun(a);
getchar();
return 0;
}
|
Java
import java.io.*;
class GFG {
static void fun(int x)
{
if(x > 0)
{
fun(--x);
System.out.print(x + " ");
fun(--x);
}
}
public static void main (String[] args)
{
int a = 4;
fun(a);
}
}
|
Python3
def fun(x):
if(x > 0):
x -= 1
fun(x)
print(x , end=" ")
x -= 1
fun(x)
a = 4
fun(a)
|
C#
using System;
class GFG{
static void fun(int x)
{
if(x > 0)
{
fun(--x);
Console.Write(x + " ");
fun(--x);
}
}
static public void Main ()
{
int a = 4;
fun(a);
}
}
|
Javascript
<script>
function fun(x)
{
if (x > 0)
{
x -= 1
fun(x)
document.write(x + " ");
x -= 1
fun(x)
}
}
let a = 4;
fun(a)
</script>
|
Time complexity: O(2n)
Auxiliary Space: O(n), since n extra space has been taken.
fun(4);
/
fun(3), print(3), fun(2)(prints 0 1)
/
fun(2), print(2), fun(1)(prints 0)
/
fun(1), print(1), fun(0)(does nothing)
/
fun(0), print(0), fun(-1) (does nothing)
Question 2
Predict the output of the following program. What does the following fun() do in general?
C++
#include <iostream>
using namespace std;
int fun(int a[],int n)
{
int x;
if(n == 1)
return a[0];
else
x = fun(a, n - 1);
if(x > a[n - 1])
return x;
else
return a[n - 1];
}
int main()
{
int arr[] = {12, 10, 30, 50, 100};
cout << " " << fun(arr, 5) <<" ";
getchar();
return 0;
}
|
C
#include<stdio.h>
int fun(int a[],int n)
{
int x;
if(n == 1)
return a[0];
else
x = fun(a, n-1);
if(x > a[n-1])
return x;
else
return a[n-1];
}
int main()
{
int arr[] = {12, 10, 30, 50, 100};
printf(" %d ", fun(arr, 5));
getchar();
return 0;
}
|
Java
import java.io.*;
class GFG {
static int fun(int a[],int n)
{
int x;
if(n == 1)
return a[0];
else
x = fun(a, n - 1);
if(x > a[n - 1])
return x;
else
return a[n - 1];
}
public static void main (String[] args)
{
int arr[] = {12, 10, 30, 50, 100};
System.out.println(" "+fun(arr, 5)+" ");
}
}
|
Python3
def fun( a, n):
if(n == 1):
return a[0]
else:
x = fun(a, n - 1)
if(x > a[n - 1]):
return x
else:
return a[n - 1]
arr = [12, 10, 30, 50, 100]
print(fun(arr, 5))
|
C#
using System;
public class GFG{
static int fun(int[] a,int n)
{
int x;
if(n == 1)
return a[0];
else
x = fun(a, n - 1);
if(x > a[n - 1])
return x;
else
return a[n - 1];
}
static public void Main ()
{
int[] arr = {12, 10, 30, 50, 100};
Console.Write(" "+fun(arr, 5)+" ");
}
}
|
Javascript
<script>
function fun(a, n)
{
var x;
if(n == 1)
return a[0];
else
x = fun(a, n - 1);
if(x > a[n - 1])
return x;
else
return a[n - 1];
}
var arr = [12, 10, 30, 50, 100];
document.write(fun(arr, 5));
</script>
|
Time complexity: O(n)
Auxiliary Space: O(n)
fun() returns the maximum value in the input array a[] of size n.
Question 3
Predict the output of the following program. What does the following fun() do in general?
C++
#include <iostream>
using namespace std;
int fun(int i)
{
if (i % 2) return (i++);
else return fun(fun(i - 1));
}
int main()
{
cout << " " << fun(200) << " ";
getchar();
return 0;
}
|
C
int fun(int i)
{
if ( i%2 ) return (i++);
else return fun(fun( i - 1 ));
}
int main()
{
printf(" %d ", fun(200));
getchar();
return 0;
}
|
Java
import java.io.*;
class GFG {
static int fun(int i)
{
if (i % 2 == 1) return (i++);
else return fun(fun(i - 1));
}
public static void main (String[] args) {
System.out.println(" " + fun(200) + " ");
}
}
|
Python3
def fun(i) :
if (i % 2 == 1) :
i += 1
return (i - 1)
else :
return fun(fun(i - 1))
print(fun(200))
|
C#
using System;
class GFG{
static int fun(int i)
{
if (i % 2 == 1) return (i++);
else return fun(fun(i - 1));
}
static public void Main ()
{
Console.WriteLine(fun(200));
}
}
|
Javascript
<script>
function fun(i)
{
if (i % 2 == 1)
return (i++);
else
return fun(fun(i - 1));
}
document.write(fun(200));
</script>
|
If n is odd, then return n, else returns (n-1). Eg., for n = 12, you get 11 and for n = 11 you get 11. The statement “return i++;” returns the value of i only as it is a post-increment.
Time complexity: O(n)
Auxiliary Space: O(1)
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