C++ Programming Searching for Patterns Set 1 Naive Pattern Searching

Given a text txt[0..n-1] and a pattern pat[0..m-1], write a function search(char pat[], char txt[]) that prints all occurrences of pat[] in txt[]. You may assume that n > m.

Examples:

Input:  txt[] = "THIS IS A TEST TEXT"
        pat[] = "TEST"
Output: Pattern found at index 10

Input:  txt[] =  "AABAACAADAABAABA"
        pat[] =  "AABA"
Output: Pattern found at index 0
        Pattern found at index 9
        Pattern found at index 12

Pattern searching is an important problem in computer science. When we do search for a string in notepad/word file or browser or database, pattern searching algorithms are used to show the search results.

Naive Pattern Searching:
Slide the pattern over text one by one and check for a match. If a match is found, then slides by 1 again to check for subsequent matches.

C++ Programming

// C++ program for Naive Pattern Searching algorithm
#include<stdio.h>
#include<string.h>
 
void search(char *pat, char *txt)
{
    int M = strlen(pat);
    int N = strlen(txt);
  
    /* A loop to slide pat[] one by one */
    for (int i = 0; i <= N - M; i++)
    {
        int j;
  
        /* For current index i, check for pattern match */
        for (j = 0; j < M; j++)
            if (txt[i+j] != pat[j])
                break;
 
        if (j == M)  // if pat[0...M-1] = txt[i, i+1, ...i+M-1]
           printf("Pattern found at index %d \n", i);
    }
}
  
/* Driver program to test above function */
int main()
{
   char txt[] = "AABAACAADAABAAABAA";
   char pat[] = "AABA";
   search(pat, txt);
   return 0;
}