Skip to content
Related Articles
Recursive function to do substring search
• Difficulty Level : Easy
• Last Updated : 23 May, 2019

Given a text txt[] and a pattern pat[], write a recursive function “contains(char pat[], char txt[])” that returns true if pat[] is present in txt[], otherwise false.

Examples:

```1) Input:   txt[] =  "THIS IS A TEST TEXT"
pat[] = "TEST"
Output:  true

2) Input:  txt[] =  "geeksforgeeks"
pat[] = "quiz"
Output:  false;```

We strongly recommend to minimize the browser and try this yourself first.

Below is recursive algorithm.

```contains(tex[], pat[])
1) If the current character is the last character of the text, but pat
has more characters, return false.

2) Else If the current character is the last character of the pattern,
then return true

3) Else If current characters of pat and text match, then
return contains(text + 1, pat + 1);

4) Else If current characters of pat and text don't match
return contains(text + 1, pat);
```

Below is the implementation of the above algorithm.

## C++

 `// Recursive C++ program to find if a given pattern is ``// present in a text``#include``using` `namespace` `std;`` ` `bool` `exactMatch(``char` `*text, ``char` `*pat)``{``    ``if` `(*text == ``'\0'` `&& *pat != ``'\0'``)``        ``return` `false``;`` ` `    ``// Else If last character of pattern reaches``    ``if` `(*pat == ``'\0'``)``        ``return` `true``;`` ` `    ``if` `(*text == *pat)``        ``return` `exactMatch(text + 1, pat + 1);`` ` `    ``return` `false``;``}`` ` `// This function returns true if 'text' contain 'pat'``bool` `contains(``char` `*text, ``char` `*pat)``{``    ``// If last character of text reaches``    ``if` `(*text == ``'\0'``)``        ``return` `false``;`` ` `    ``// If current characters of pat and text match``    ``if` `(*text == *pat)``        ``if``(exactMatch(text, pat))``            ``return` `1;``        ``else``          ``return` `contains(text + 1, pat);`` ` `    ``// If current characters of pat and tex don't match``    ``return` `contains(text + 1, pat);``}`` ` `// Driver program to test above function``int` `main()``{``    ``cout << contains(``"geeksforgeeks"``, ``"geeks"``) << endl;``    ``cout << contains(``"geeksforgeeks"``, ``"geeksquiz"``) << endl;``    ``cout << contains(``"geeksquizgeeks"``, ``"quiz"``) << endl;``    ``return` `0;``}`

## Python3

 `# Recursive Python3 program to find if a given pattern is ``# present in a text`` ` `def` `exactMatch(text, pat, text_index, pat_index):``    ``if` `text_index ``=``=` `len``(text) ``and` `pat_index !``=` `len``(pat):``        ``return` `0``  ` `    ``# Else If last character of pattern reaches``    ``if` `pat_index ``=``=` `len``(pat):``        ``return` `1``  ` `    ``if` `text[text_index] ``=``=` `pat[pat_index]:``        ``return` `exactMatch(text, pat, text_index``+``1``, pat_index``+``1``)``  ` `    ``return` `0`` ` `  ` `# This function returns true if 'text' contain 'pat'``def` `contains(text, pat, text_index, pat_index):``    ``# If last character of text reaches``    ``if` `text_index ``=``=` `len``(text):``        ``return` `0``  ` `    ``# If current characters of pat and text match``    ``if` `text[text_index] ``=``=` `pat[pat_index]:``        ``if` `exactMatch(text, pat, text_index, pat_index):``            ``return` `1``        ``else``:``            ``return` `contains(text, pat, text_index``+``1``, pat_index)``  ` `    ``# If current characters of pat and tex don't match``    ``return` `contains(text , pat, text_index``+``1``, pat_index)``  ` `# Driver program to test the above function`` ` `print``(contains(``"geeksforgeeks"``, ``"geeks"``, ``0``, ``0``))``print``(contains(``"geeksforgeeks"``, ``"geeksquiz"``, ``0``, ``0``))``print``(contains(``"geeksquizgeeks"``, ``"quiz"``, ``0``, ``0``))`` ` `# This code is contributed by ankush_953.`

Output:
```1
0
1```

This article is contributed by Bhupinder. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with industry experts, please refer DSA Live Classes

My Personal Notes arrow_drop_up