Recursive function to do substring search

30 Jun, 2022
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++
Java
Python3
Javascript
// Recursive C++ program to find if a given pattern is// present in a text#include<iostream>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 functionint main(){ cout << contains("geeksforgeeks", "geeks") << endl; cout << contains("geeksforgeeks", "geeksquiz") << endl; cout << contains("geeksquizgeeks", "quiz") << endl; return 0;}
// Recursive Java program to find if a given pattern is// present in a text class GFG {    static int exactMatch(String text, String pat, int text_index, int pat_index) {        if (text_index == text.length() && pat_index != pat.length())            return 0;         // Else If last character of pattern reaches        if (pat_index == pat.length())            return 1;         if (text.charAt(text_index) == pat.charAt(pat_index))            return exactMatch(text, pat, text_index + 1, pat_index + 1);         return 0;    }     // This function returns true if 'text' contain 'pat'    static int contains(String text, String pat, int text_index, int pat_index) {        // If last character of text reaches        if (text_index == text.length())            return 0;         // If current characters of pat and text match        if (text.charAt(text_index) == pat.charAt(pat_index)) {            if (exactMatch(text, pat, text_index, pat_index) == 1)                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    public static void main(String args[]) {        System.out.println(contains("geeksforgeeks", "geeks", 0, 0));        System.out.println(contains("geeksforgeeks", "geeksquiz", 0, 0));        System.out.println(contains("geeksquizgeeks", "quiz", 0, 0));     }}// This code is contributed by Saurabh Jaiswal
# 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.
<script> // Recursive JavaScript program to find if a given pattern is// present in a text function exactMatch(text, pat, text_index, pat_index){    if(text_index == text.length && pat_index != pat.length)        return 0      // Else If last character of pattern reaches    if(pat_index == pat.length)        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'function contains(text, pat, text_index, pat_index){    // If last character of text reaches    if(text_index == text.length)        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 document.write(contains("geeksforgeeks", "geeks", 0, 0),"</br>")document.write(contains("geeksforgeeks", "geeksquiz", 0, 0),"</br>")document.write(contains("geeksquizgeeks", "quiz", 0, 0),"</br>") // This code is contributed by shinjanpatra. </script>
Output:
1
0
1
Time Complexity : O(n*m)Auxiliary Space : O(n+m)
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
san123
ankush_953
shinjanpatra
_saurabh_jaiswal
susobhanakhuli
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