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 10Input: 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
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