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# Practice Questions for Recursion | Set 6

Question 1
Consider the following recursive C function. Let len be the length of the string s and num be the number of characters printed on the screen. Give the relation between num and len where len is always greater than 0.

## C++

 `void` `abc(``char` `*s)` `{` `    ``if``(s == ``'\0'``)` `        ``return``;` ` `  `    ``abc(s + 1);` `    ``abc(s + 1);` `    ``cout << s;    ` `}`   `// This code is contributed by shubhamsingh10`

## C

 `void` `abc(``char` `*s)` `{` `    ``if``(s == ``'\0'``)` `        ``return``;`   `    ``abc(s + 1);` `    ``abc(s + 1);` `    ``printf``(``"%c"``, s);    ` `}`

## Java

 `static` `void` `abc(``char` `*s)` `{` `    ``if``(s[``0``] == ``'\0'``)` `        ``return``;` `  `  `    ``abc(s + ``1``);` `    ``abc(s + ``1``);` `    ``System.out.print(s[``0``]);    ` `}`   `// This code is contributed by shubhamsingh10`

## Python3

 `def` `abc(s):` `    ``if``(``len``(s) ``=``=` `0``):` `        ``return` `    `  `    ``abc(s[``1``:])` `    ``abc(s[``1``:])` `    ``print``(s[``0``])` `    `  `# This code is contributed by shubhamsingh10`

## C#

 `static` `void` `abc(``char` `*s)` `{` `    ``if``(s == ``'\0'``)` `        ``return``;`   `    ``abc(s + 1);` `    ``abc(s + 1);` `    ``Console.Write(s); ` `}`   `// This code is contributed by shubhamsingh10`

## Javascript

 ``

Time complexity: O(2n)

Auxiliary Space: O(n)

The following is the relationship between num and len.

` num = 2^len-1`
```s is 1 time printed
s is 2 times printed
s is 4 times printed
s[i] is printed 2^i times
s[strlen(s)-1] is printed 2^(strlen(s)-1) times
total = 1+2+....+2^(strlen(s)-1)
= (2^strlen(s)) - 1```

For example, the following program prints 7 characters.

## C++

 `#include ` `using` `namespace` `std;`   `void` `abc(``char` `s[])` `{` `    ``if``(s == ``'\0'``)` `        ``return``;`   `    ``abc(s + 1);` `    ``abc(s + 1);` `    ``cout << s;` `}`   `int` `main()` `{` `    ``abc(``"xyz"``);` `    ``return` `0;` `}` `//This code is contributed by shubhamsingh10`

## C

 `#include`   `void` `abc(``char` `*s)` `{` `    ``if``(s == ``'\0'``)` `        ``return``;`   `    ``abc(s + 1);` `    ``abc(s + 1);` `    ``printf``(``"%c"``, s);` `}`   `int` `main()` `{` `    ``abc(``"xyz"``);` `    ``return` `0;` `}`

## Java

 `public` `class` `GFG` `{` `    ``static` `void` `abc(String s)` `    ``{` `        ``if``(s.length() == ``0``)` `            ``return``;` `     `  `        ``abc(s.substring(``1``));` `        ``abc(s.substring(``1``));` `        ``System.out.print(s.charAt(``0``));` `    ``}`   `    ``public` `static` `void` `main(String[] args) {` `        ``abc(``"xyz"``);` `    ``}` `}`   `// This code is contributed by divyeh072019`

## Python3

 `def` `abc(s):` `    ``if``(``len``(s) ``=``=` `0``):` `        ``return` `    `  `    ``abc(s[``1``:])` `    ``abc(s[``1``:])` `    ``print``(s[``0``],end``=``"")`     `# Driver code`   `abc(``"xyz"``)`   `# This code is contributed by shubhamsingh10`

## C#

 `using` `System;` `class` `GFG {` `    `  `    ``static` `void` `abc(``string` `s) ` `    ``{ ` `        ``if``(s.Length == 0) ` `            ``return``; ` `            `  `        ``abc(s.Substring(1)); ` `        ``abc(s.Substring(1)); ` `        ``Console.Write(s); ` `    ``} `   `  ``// Driver code` `  ``static` `void` `Main() {` `    ``abc(``"xyz"``);` `  ``}` `}`   `// This code is contributed by divyeshrabadiya07`

## Javascript

 ``

Thanks to bharat nag for suggesting this solution.

Question 2

## C++

 `#include ` `using` `namespace` `std;`   `int` `fun(``int` `count) ` `{ ` `    ``cout << count << endl; ` `    ``if``(count < 3) ` `    ``{ ` `        ``fun(fun(fun(++count))); ` `    ``} ` `    ``return` `count; ` `} `   `int` `main() ` `{ ` `    ``fun(1); ` `    ``return` `0; ` `}`   `// This code is contributed by Shubhamsingh10`

## C

 `#include` `int` `fun(``int` `count)` `{` `    ``printf``(``"%d\n"``, count);` `    ``if``(count < 3)` `    ``{` `      ``fun(fun(fun(++count)));` `    ``}` `    ``return` `count;` `}`   `int` `main()` `{` `    ``fun(1);` `    ``return` `0;` `}`

## Java

 `import` `java.util.*;` ` `  `class` `GFG{` `static` `int` `fun(``int` `count) ` `{ ` `    ``System.out.println(count); ` `    ``if``(count < ``3``) ` `    ``{ ` `        ``fun(fun(fun(++count))); ` `    ``} ` `    ``return` `count; ` `} `   `public` `static` `void` `main(String[] args)` `{ ` `    ``fun(``1``); ` `}` `}`   `// This code is contributed by Shubhamsingh10`

## Python3

 `def` `fun(count):` `    ``print``(count)` `    ``if``(count < ``3``):` `        ``count``+``=``1` `        ``fun(fun(fun(count))) ` `    `  `    ``return` `count ` ` `    `if` `__name__``=``=``"__main__"``:  ` `    `  `    ``fun(``1``) `   `# This code is contributed by Shubhamsingh10 `

## C#

 `using` `System;`   `class` `GFG{` `    `  `    ``static` `int` `fun(``int` `count)  ` `    ``{  ` `        ``Console.Write(count+``"\n"``);  ` `        ``if``(count < 3)  ` `        ``{  ` `            ``fun(fun(fun(++count)));  ` `        ``}  ` `        ``return` `count;  ` `    ``}  ` `      `  `    ``static` `public` `void` `Main ()` `    ``{  ` `        ``fun(1);   ` `    ``} ` `}`   `// This code is contributed by shubhamsingh10`

## Javascript

 ``

Output:

``` 1
2
3
3
3
3
3```

The main() function calls fun(1). fun(1) prints “1” and calls fun(fun(fun(2))). fun(2) prints “2” and calls fun(fun(fun(3))). So the function call sequence becomes fun(fun(fun(fun(fun(3))))). fun(3) prints “3” and returns 3 (note that the count is not incremented and no more functions are called as if the condition is not true for count 3). So the function call sequence reduces to fun(fun(fun(fun(3)))). fun(3) again prints “3” and returns 3. So the function call again reduces to fun(fun(fun(3))) which again prints “3” and reduces it to fun(fun(3)). This continues and we get “3” printed 5 times on the screen.

Time complexity: O(2n)

Auxiliary Space : O(n), since n extra space has been taken.