# Check if a string can be repeated to make another string

Given two strings a and b, the task is to check how many times the string a can be repeated to generate the string b. If b cannot be generated by repeating a then print -1.

Examples:

Input: a = “geeks”, b = “geeksgeeks”
Output: 2
“geeks” can be repeated twice to generate “geeksgeeks”

Input: a = “df”, b = “dfgrt”
Output: -1

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

• If len(b) % len(a) != 0 then print -1 as b cannot be generated by repeating a.
• Else set count = len(b) / len(a) and repeat a count number of times.
• If a = b then print count.
• Else print -1.

Below is the implementation of the above approach:

 `// CPP implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the count of repetitions  ` `// of string a to generate string b ` `int` `getCount(string a, string b) ` `{ ` ` `  `    ``// If b cannot be generated by repeating a ` `    ``if``(b.length() % a.length() != 0) ` `        ``return` `-1; ` `     `  `    ``int` `count = b.length() /a.length(); ` ` `  `    ``// Repeat a count number of times ` `    ``string str = ``""``; ` `    ``for``(``int` `i = 0; i < count; i++) ` `    ``{ ` `        ``str = str + a; ` `    ``} ` `    ``if``(str == b) ` `        ``return` `count; ` `     `  `    ``return` `-1;  ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string a = ``"geeks"``; ` `    ``string b = ``"geeksgeeks"``; ` `    ``cout << (getCount(a, b)); ` `    ``return` `0; ` `} ` ` `  `// This code is contributed by ` `// Surendra_Gangwar `

 `// Java implementation of the approach  ` ` `  `class` `GfG ` `{ ` ` `  `    ``// Function to return the count of repetitions  ` `    ``// of string a to generate string b  ` `    ``static` `int` `getCount(String a, String b)  ` `    ``{  ` `        ``// If b cannot be generated by repeating a  ` `        ``if``(b.length() % a.length() != ``0``)  ` `            ``return` `-``1``;  ` `         `  `        ``int` `count = b.length() / a.length();  ` `     `  `        ``// Repeat a count number of times  ` `        ``String str = ``""``;  ` `        ``for``(``int` `i = ``0``; i < count; i++)  ` `        ``{  ` `            ``str = str + a;  ` `        ``} ` `         `  `        ``if``(str.equals(b))  ` `            ``return` `count;  ` `         `  `        ``return` `-``1``;  ` `    ``}  ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String []args) ` `    ``{ ` `        ``String a = ``"geeks"``;  ` `        ``String b = ``"geeksgeeks"``;  ` `        ``System.out.println(getCount(a, b)); ` `    ``} ` `} ` `     `  `// This code is contributed by Rituraj Jain `

 `# Python3 implementation of the approach ` ` `  `# Function to return the count of repetitions  ` `# of string a to generate string b ` `def` `getCount(a, b): ` `     `  `    ``# If b cannot be generated by repeating a ` `    ``if``(``len``(b) ``%` `len``(a) !``=` `0``): ` `        ``return` `-``1``; ` `     `  `    ``count ``=` `int``(``len``(b) ``/` `len``(a)) ` `     `  `    ``# Repeat a count number of times ` `    ``a ``=` `a ``*` `count ` `     `  `    ``if``(a ``=``=` `b): ` `        ``return` `count ` `     `  `    ``return` `-``1``; ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``a ``=` `'geeks'` `    ``b ``=` `'geeksgeeks'` `    ``print``(getCount(a, b)) `

 `// C# implementation of the approach  ` `using` `System; ` ` `  `class` `GfG ` `{ ` ` `  `    ``// Function to return the count of repetitions  ` `    ``// of string a to generate string b  ` `    ``static` `int` `getCount(String a, String b)  ` `    ``{  ` `        ``// If b cannot be generated by repeating a  ` `        ``if``(b.Length % a.Length != 0)  ` `            ``return` `-1;  ` `         `  `        ``int` `count = b.Length / a.Length;  ` `     `  `        ``// Repeat a count number of times  ` `        ``String str = ``""``;  ` `        ``for``(``int` `i = 0; i < count; i++)  ` `        ``{  ` `            ``str = str + a;  ` `        ``} ` `         `  `        ``if``(str.Equals(b))  ` `            ``return` `count;  ` `         `  `        ``return` `-1;  ` `    ``}  ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String []args) ` `    ``{ ` `        ``String a = ``"geeks"``;  ` `        ``String b = ``"geeksgeeks"``;  ` `        ``Console.WriteLine(getCount(a, b)); ` `    ``} ` `} ` ` `  `// This code contributed by Rajput-Ji `

 ` `

Output:
```2
```

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

Front and Back End Web Developer Android Developer Python and C++ Coder Networking Geek

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 Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :