PHP Program for Naive algorithm for Pattern Searching

Write a PHP program for a given text string with length n and a pattern with length m, the task is to print all occurrences of the pattern in text.
Note: You may assume that n > m.

Examples:

Input:  text = “THIS IS A TEST TEXT”, pattern = “TEST”
Output: Pattern found at index 10

Input:  text =  “AABAACAADAABAABA”, pattern = “AABA”
Output: Pattern found at index 0, Pattern found at index 9, Pattern found at index 12

PHP Program for Naive Pattern Searching algorithm:

Slide the pattern over text one by one and check for a match. If a match is found, then slide by 1 again to check for subsequent matches.

PHP

<?php
// PHP program for Naive Pattern
// Searching algorithm

function search($pat, $txt)
{
    $M = strlen($pat);
    $N = strlen($txt);

    // A loop to slide pat[] 
    // one by one 
    for ($i = 0; $i <= $N - $M; $i++)
    {

        // For current index i, 
        // check for pattern match 
        for ($j = 0; $j < $M; $j++)
            if ($txt[$i + $j] != $pat[$j])
                break;

        // if pat[0...M-1] = 
        // txt[i, i+1, ...i+M-1]
        if ($j == $M) 
            echo "Pattern found at index ", $i."\n";
    }
}

    // Driver Code
    $txt = "AABAACAADAABAAABAA";
    $pat = "AABA";
    search($pat, $txt);
    
// This code is contributed by Sam007
?>

Output

Pattern found at index 0
Pattern found at index 9
Pattern found at index 13

Time Complexity: O(N²)
Auxiliary Space: O(1)

Complexity Analysis of Naive algorithm for Pattern Searching:

Best Case: O(n)

• When the pattern is found at the very beginning of the text (or very early on).
• The algorithm will perform a constant number of comparisons, typically on the order of O(n) comparisons, where n is the length of the pattern.

Worst Case: O(n²)

• When the pattern doesn’t appear in the text at all or appears only at the very end.
• The algorithm will perform O((n-m+1)*m) comparisons, where n is the length of the text and m is the length of the pattern.
• In the worst case, for each position in the text, the algorithm may need to compare the entire pattern against the text.
• Naive algorithm for Pattern Searching

Please refer complete article on Naive algorithm for Pattern Searching for more details!

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