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Pattern Searching using C++ library

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  • Difficulty Level : Easy
  • Last Updated : 12 Dec, 2021
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Given a text txt[0..n-1] and a pattern pat[0..m-1], write a function that prints all occurrences of pat[] in txt[]. You may assume that n > m.
Examples: 
 

Input : txt[] = "geeks for geeks"
        pat[] = "geeks"
Output : Pattern found at index 0
         Pattern found at index 10

Input : txt[] = "aaaa"
        pat[] = "aa"
Output : Pattern found at index 0
         Pattern found at index 1
         Pattern found at index 2

The idea is to use find() in C++ string class.

CPP




// CPP program to print all occurrences of a pattern
// in a text
#include <bits/stdc++.h>
using namespace std;
 
void printOccurrences(string txt, string pat)
{
    int found = txt.find(pat);
    while (found != string::npos) {
        cout << "Pattern found at index " << found << endl;
        found = txt.find(pat, found + 1);
    }
}
 
int main()
{
    string txt = "aaaa", pat = "aa";
    printOccurrences(txt, pat);
    return 0;
}


Output: 

Pattern found at index 0
Pattern found at index 1
Pattern found at index 2

 

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