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C Program for Naive algorithm for Pattern Searching
Pattern matching in C− We have to find if a string is present in another string, as an example, the string "algorithm” is present within the string "naive algorithm". If it is found, then its location (i.e. position it is present at) is displayed. We tend to create a function that receives 2 character arrays and returns the position if matching happens otherwise returns -1.
Input: txt = "HERE IS A NICE CAP" pattern = "NICE" Output: Pattern found at index 10 Input: txt = "XYZXACAADXYZXYZX" pattern = "XYZX" Output: Pattern found at index 0 Pattern found at index 9 Pattern found at index 12
We are solving this problem with Naive Pattern Searching. This algorithm is useful for smaller texts. Naive is a simple and inefficient way to see wherever one string occurs within another is to examine every place it could be at, one by one, to examine if it's there.
The time complexity of the Naive Algorithm is O(mn), where m is the size of the pattern to be searched and n is the size of the container string.
Pattern searching is a very crucial problem in computer science. Whenever we seek for a string in notepad/word file or browser or database or in some information, pattern searching algorithms are used to show the search results.
Algorithm
naive_algorithm(pattern, text)
Input − The text and the pattern
Output − locations, where the pattern is present in the text
Start pat_len := pattern Size str_len := string size for i := 0 to (str_len - pat_len), do for j := 0 to pat_len, do if text[i+j] ≠ pattern[j], then break if j == patLen, then display the position i, as there pattern found End
Example
#include <stdio.h>
#include <string.h>
int main (){
char txt[] = "tutorialsPointisthebestplatformforprogrammers";
char pat[] = "a";
int M = strlen (pat);
int N = strlen (txt);
for (int i = 0; i <= N - M; i++){
int j;
for (j = 0; j < M; j++)
if (txt[i + j] != pat[j])
break;
if (j == M)
printf ("Pattern matches at index %d
", i);
}
return 0;
}Output
Pattern matches at 6 Pattern matches at 25 Pattern matches at 39
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