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Knuth-Morris-Pratt is an Algorithm for searching a text for a string. It's a very commonly used algorithm and is very fast. TODO: write about how it works.
Here is a Delphi implementation of the kmp search algorithm.
function kmp_search_next( const W, S: string; const T: array of Integer): Integer; var m, i: Integer; begin i := 1; m := 1; while ( ( ( m + i ) <= Length( S ) ) and ( i <= Length( W ) ) ) do begin if ( S[m + i] = W[i] ) then begin Inc( i ); end else begin m := m + ( i - T[i] ); if ( i > 1 ) then i := T[i]; end; end; if m = Length( S ) then Result := 0 else Result := m; end;
function kmp_table( W: string ): array of Integer; var i, j: Integer; T: array of Integer; begin i := 3; j := 1; SetLength( T, Length( W ) + 1 ); t := 0;
if ( Length( W ) > 1 ) then t := 1; while ( i <= Length( W ) ) do begin if ( W[i - 1] = W[j] ) then begin T[i] := j + 1; Inc( j ); Inc( i ); end else if ( j > 1 ) then begin j := T[j]; end else begin T[i] := 1; Inc( i ); j := 1; end; end; Result := T; end;
Use those two functions like this:
var str_to_search_for: string; str_to_search_in: string; begin str_to_search_for := 'Word(s)'; str_to_search_in := 'String in which you will search for the word(s)'; kmp_search_next( str_to_search_for, str_to_search_in, kmp_table( str_to_search_for ) ); end;
And the result of kmp_search_next will be the position of the word you searched for. If it isn't found it will return zero.
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